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  • 1.
    Ahlstrand, Emma
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Spångberg, Daniel
    Uppsala University.
    Hermansson, Kersti
    Uppsala University.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Interaction energies between metal ions (Zn2+ and Cd2+) and biologically relevant ligands2013In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 113, no 23, p. 2554-2562Article in journal (Refereed)
    Abstract [en]

    Interactions between the group XII metals Zn2+ and Cd2+ and amino acid residues play an important role in biology due to the prevalence of the first and the toxicity of the second. Estimates of the interaction energies between the ions and relevant residues in proteins are however difficult to obtain. This study reports on calculated interaction energy curves for small complexes of Zn2+ or Cd2+ and amino acid mimics (acetate, methanethiolate, and imidazole) or water. Given that many applications and models (e.g., force fields, solvation models, etc.) begin with and rely on an accurate description of gas-phase interaction energies, this is where our focus lies in this study. Four density functional theory (DFT)-functionals and MP2 were used to calculate the interaction energies not only at the respective equilibrium distances but also at a relevant range of ion–ligand separation distances. The calculated values were compared with those obtained by CCSD(T). All DFT-methods are found to overestimate the magnitude of the interaction energy compared to the CCSD(T) reference values. The deviation was analyzed in terms of energy components from localized molecular orbital energy decomposition analysis scheme and is mostly attributed to overestimation of the polarization energy. MP2 shows good agreement with CCSD(T) [root mean square error (RMSE) = 1.2 kcal/mol] for the eight studied complexes at equilibrium distance. Dispersion energy differences at longer separation give rise to increased deviations between MP2 and CCSD(T) (RMSE = 6.4 kcal/mol at 3.0 Å). Overall, the results call for caution in applying DFT methods to metalloprotein model complexes even with closed-shell metal ions such as Zn2+ and Cd2+, in particular at ion–ligand separations that are longer than the equilibrium distances.

  • 2.
    Ahlstrand, Emma
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Zukerman Schpector, Julio
    Universidade Federal de São Carlos, Brazil.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Computer simulations of alkali-acetate solutions: Accuracy of the forcefields in difference concentrations2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, p. 1-10, article id 194102Article in journal (Refereed)
    Abstract [en]

    When proteins are solvated in electrolyte solutions that contain alkali ions, the ions interact mostlywith carboxylates on the protein surface. Correctly accounting for alkali-carboxylate interactionsis thus important for realistic simulations of proteins. Acetates are the simplest carboxylates thatare amphipathic, and experimental data for alkali acetate solutions are available and can be comparedwith observables obtained from simulations. We carried out molecular dynamics simulations of alkali acetate solutions using polarizable and non-polarizable forcefields and examined the ionacetateinteractions. In particular, activity coefficients and association constants were studied in a range of concentrations (0.03, 0.1, and 1M). In addition, quantum-mechanics (QM) based energy decomposition analysis was performed in order to estimate the contribution of polarization, electrostatics, dispersion, and QM (non-classical) effects on the cation-acetate and cation-water interactions. Simulations of Li-acetate solutions in general overestimated the binding of Li+ and acetates. In lower concentrations, the activity coefficients of alkali-acetate solutions were too high, which is suggested to be due to the simulation protocol and not the forcefields. Energy decomposition analysis suggested that improvement of the forcefield parameters to enable accurate simulations of Li-acetate solution scan be achieved but may require the use of a polarizable forcefield. Importantly, simulations with some ion parameters could not reproduce the correct ion-oxygen distances, which calls for caution in thechoice of ion parameters when protein simulations are performed in electrolyte solutions.

  • 3.
    Becconi, Olga
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences. University of Cagliari, Italy.
    Ahlstrand, Emma
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Salis, Andrea
    University of Cagliari, Italy.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Protein-ion Interactions: Simulations of Bovine Serum Albumin in Physiological Solutions of NaCl, KCl and LiCl2017In: Israel Journal of Chemistry, ISSN 0021-2148, Vol. 57, no 5, p. 403-412Article in journal (Refereed)
    Abstract [en]

    Specific interactions that depend on the nature of electrolytes are observed when proteins and other molecules are studied by potentiometric, spectroscopic and theoretical methods at high salt concentrations. More recently, it became clear that such interactions may also be observed in solutions that can be described by the Debye-Hückel theory, i.e., at physiological (0.1 mol dm−3) and lower concentrations. We carried out molecular dynamics simulations of bovine serum albumin in physiological solutions at T=300 and 350 K. Analysis of the simulations revealed some differences between LiCl solutions and those of NaCl and KCl. The binding of Li+ ions to the protein was associated with a negative free energy of interaction whereas much fewer Na+ and K+ ions were associated with the protein surface. Interestingly, unlike other proteins BSA does not show a preference to Na+ over K+. Quantum chemical calculations identified a significant contribution from polarisation to the hydration of Li+ and (to a lesser degree) Na+, which may indicate that polarisable force-fields will provide more accurate results for such systems.

  • 4.
    Cournia, Zoe
    et al.
    Academy of Athens, Greece.
    Allen, Toby W.
    University of California, USA ; RMIT University, Australia.
    Andricioaei, Ioan
    University of California, USA.
    Antonny, Bruno
    Université de Nice Sophia-Antipolis, France.
    Baum, Daniel
    Zuse Institute Berlin, Germany.
    Brannigan, Grace
    Rutgers University-Camden, USA.
    Buchete, Nicolae-Viorel
    University College Dublin, Ireland.
    Deckman, Jason T.
    University of California, USA.
    Delemotte, Lucie
    Temple University, USA.
    del Val, Coral
    University of Granada, Spain.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Gkeka, Paraskevi
    Academy of Athens, Greece.
    Hege, Hans-Christian
    Zuse Institute Berlin, Germany.
    Hénin, Jérôme
    IBPC and CNRS, France.
    Kasimova,, Marina A.
    Université de Lorraine, France ; Lomonosov Moscow State University, Russia.
    Kolocouris, Antonios
    University of Athens, Greece.
    Klein, Michael L.
    Temple University, USA.
    Khalid, Syma
    University of Southampton, UK.
    Lemieux, M. Joanne
    University of Alberta, Canada.
    Lindow, Norbert
    Zuse Institute Berlin, Germany.
    Mahua, Roy
    University of California, USA.
    Selent, Jana
    Universitat Pompeu Fabra, Spain.
    Tarek, Mounir
    Université de Lorraine, France ; CNRS SRSMC, France.
    Tofoleanu, Florentina
    University College Dublin, Ireland.
    Stefano, Vanni
    Université de Nice Sophia-Antipolis, Greece.
    Sinisa, Urban
    Johns Hopkins University School of Medicine, USA.
    Wales, David J.
    University of Cambridge, UK.
    Smith, Jeremy C.
    Oak Ridge National Laboratory, USA.
    Bondar, Ana-Nicoleta
    Freie Universität Berlin, Germany.
    Membrane Protein Structure, Function, and Dynamics: a Perspective from Experiments and Theory2015In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 248, no 4, p. 611-640Article in journal (Refereed)
    Abstract [en]

    Membrane proteins mediate processes that are fundamental for the flourishing of biological cells. Membrane-embedded transporters move ions and larger solutes across membranes; receptors mediate communication between the cell and its environment and membrane-embedded enzymes catalyze chemical reactions. Understanding these mechanisms of action requires knowledge of how the proteins couple to their fluid, hydrated lipid membrane environment. We present here current studies in computational and experimental membrane protein biophysics, and show how they address outstanding challenges in understanding the complex environmental effects on the structure, function, and dynamics of membrane proteins.

  • 5.
    Friedman, Ran
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Ions and the protein surface revisited: extensive molecular dynamics simulations and analysis of protein structures in alkali-chloride solutions2011In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, p. 9213-9223Article in journal (Refereed)
    Abstract [en]

    Proteins interact with ions in various ways. The surface of proteins has an innate capability to bind ions, and it is also influenced by the screening of the electrostatic potential owing to the presence of salts in the bulk solution. Alkali metal ions and chlorides interact with the protein surface, but such interactions are relatively weak and often transient. In this paper, computer simulations and analysis of protein structures are used to characterize the interactions between ions and the protein surface. The results show that the ion-binding properties of protein residues are highly variable. For example, alkali metal ions are more often associated with aspartate residues than with glutamates, whereas chlorides are most likely to be located near arginines. When comparing NaCl and KCl solutions, it was found that certain surface residues attract the anion more strongly in NaCl. This study demonstrates that protein–salt interactions should be accounted for in the planning and execution of experiments and simulations involving proteins, particularly if subtle structural details are sought after.

  • 6.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Membrane-Ion Interactions2018In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 251, no 3, p. 453-460Article in journal (Refereed)
    Abstract [en]

    Biomembranes assemble and operate at the interface with electrolyte solutions. Interactions between ions in solutions and the lipid affect the membrane structure, dynamics and electrostatic potential. In this article, I review some of the experimental and computational methods that are used to study membrane-ions interactions. Experimental methods that account for membrane-ion interactions directly and indirectly are presented first. Then, studies in which molecular dynamics simulations were used to gain an understanding of membrane-ion interactions are surveyed. Finally, the current view on membrane-ion interactions and their significance is briefly discussed.

  • 7.
    Friedman, Ran
    University of Zürich, Switzerland.
    Proton Transfer on the Molecular Surface of Proteins and Model Systems2009In: Israel Journal of Chemistry, ISSN 0021-2148, Vol. 49, no 2, p. 149-153Article in journal (Refereed)
    Abstract [en]

    Proton transfer (PT) reactions take place oil the molecular Surface of proteins, membranes, ionic polymers, and other molecules. The rates of the reactions can be followed experimentally, while the atomistic details can be elucidated by molecular modeling. This manuscript gives a brief overview of the use of computer simulations and molecular modeling, in conjuction with experiments, to study PT reactions oil the surface of solvated molecules. An integrative approach is discussed, where molecular dynamics simulations are performed with a protein, and quantum-mechanics-based calculations are performed oil a small molecule. The simulation results allow the identification of the necessary conditions that yield PT reactions oil the molecular surface. The reactions are efficient when they involve a donor and acceptor located a few A apart and under the influence of a negative electrostatic field. In proton-pumping proteins, it is possible to identify such conditions a priori and locate proton-attracting antenna domains without the need to mutate each potential donor and acceptor. Based on density functional theory calculations, the arrangement of water molecules that interconnect the donor and acceptor moieties is suggested as the rate-limiting step for proton transfer on the molecular surface.

  • 8.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Simulations of Biomolecules in Electrolyte Solutions2019In: Advanced Theory and Simulations, E-ISSN 2513-0390, Vol. 2, no 4, p. 1-10, article id 1800163Article in journal (Refereed)
    Abstract [en]

    Biomolecules including proteins, lipid membranes, and nucleic acids operate at an aqueous milieu that includes solvated ions. The interactions with ions affect biomolecules in different ways depending on the nature of the solute and the type of the ions. The dynamic nature of small soluble ions makes it difficult to follow them by structural methods. Consequently, theories were developed to explain how biomolecules interact in an environment that includes electrolytes. Moreover, simulations studies are often used to study such systems at the molecular or atomistic level. The status of the field, and inparticular of simulation studies, is the subject of this progress report.

  • 9.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    The molecular mechanism behind resistance of the kinase FLT3 to the inhibitor quizartinib2017In: Proteins: Structure, Function, and Bioinformatics, ISSN 0887-3585, E-ISSN 1097-0134, Vol. 85, no 11, p. 2143-2152Article in journal (Refereed)
    Abstract [en]

    Fms-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase that is a drug target for leukemias. Several potent inhibitors of FLT3 exist, and bind to the inactive form of the enzyme. Unfortunately, resistance due to mutations in the kinase domain of FLT3 limits the therapeutic effects of these inhibitors. As in many other cases, it is not straightforward to explain why certain mutations lead to drug resistance. Extensive fully atomistic molecular dynamics (MD) simulations of FLT3 were carried out with an inhibited form (FLT-quizartinib complex), a free (apo) form, and an active conformation. In all cases, both the wild type (wt) proteins and two resistant mutants (D835F and Y842H) were studied. Analysis of the simulations revealed that impairment of protein-drug interactions cannot explain the resistance mutations in question. Rather, it appears that the active state of the mutant forms is perturbed by the mutations. It is therefore likely that perturbation of deactivation of the protein (which is necessary for drug binding) is responsible for the reduced affinity of the drug to the mutants. Importantly, this study suggests that it is possible to explain the source of resistance by mutations in FLT3 by an analysis of unbiased MD simulations.

  • 10.
    Friedman, Ran
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Boye, Kjetil
    Flatmark, Kjersti
    Molecular modelling and simulations in cancer research2013In: Biochimica et Biophysica Acta. CR. Reviews on Cancer, ISSN 0304-419X, E-ISSN 1879-2561, Vol. 1836, no 1, p. 1-14Article, review/survey (Refereed)
    Abstract [en]

    The complexity of cancer and the vast amount of experimental data available have made computer-aided approaches necessary. Biomolecular modelling techniques are becoming increasingly easier to use, whereas hardware and software are becoming better and cheaper. Cross-talk between theoretical and experimental scientists dealing with cancer-research from a molecular approach, however, is still uncommon. This is in contrast to other fields, such as amyloid-related diseases, where molecular modelling studies are widely acknowledged. The aim of this review paper is therefore to expose some of the more common approaches in molecular modelling to cancer scientists in simple terms, illustrating success stories while also revealing the limitations of computational studies at the molecular level.

  • 11.
    Friedman, Ran
    et al.
    Department of Biochemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich .
    Caflisch, A
    Discovery of plasmepsin inhibitors by fragment-based docking and consensus scoring2009In: ChemMedChem, ISSN 1860-7179, E-ISSN 1860-7187, Vol. 4, no 8, p. 1317-1326Article in journal (Refereed)
    Abstract [en]

    Plasmepsins (PMs) are essential proteases of the plasmodia parasites and are therefore promising targets for developing drugs against malaria. We have discovered six inhibitors of PM II by high-throughput fragment-based docking of a diversity set of ∼40 000 molecules, and consensus scoring with force field energy functions. Using the common scaffold of the three most active inhibitors (IC50=2–5 μM), another seven inhibitors were identified by substructure search. Furthermore, these 13 inhibitors belong to at least three different classes of compounds. The in silico approach was very effective since a total of 13 active compounds were discovered by testing only 59 molecules in an enzymatic assay. This hit rate is about one to two orders of magnitude higher than those reported for medium- and high-throughput screening techniques in vitro. Interestingly, one of the inhibitors identified by docking was halofantrine, an antimalarial drug of unknown mechanism. Explicit water molecular dynamics simulations were used to discriminate between two putative binding modes of halofantrine in PM II.

  • 12.
    Friedman, Ran
    et al.
    University of Zürich, Switzerland.
    Caflisch, A
    On the orientation of the catalytic dyad in aspartic proteases2010In: Proteins: Structure, Function, and Bioinformatics, ISSN 0887-3585, E-ISSN 1097-0134, Vol. 78, no 6, p. 1575-1582Article in journal (Refereed)
    Abstract [en]

    The recent re-refinement of the X-ray structure of apo plasmepsin II from Plasmodium falciparum suggests that the two carboxylate groups in the catalytic dyad are noncoplanar, (Robbins et al., Acta Crystallogr D Biol Crystallogr 2009;65: 294–296) in remarkable contrast with the vast majority of structures of aspartic proteases. Here, evidence for the noncoplanarity of the catalytic aspartates is provided by analysis of multiple explicit water molecular dynamics (MD) simulations of plasmepsin II, human β-secretase, and HIV-protease. In the MD runs of plasmepsin II, the angle between the planes of the two carboxylates of the catalytic dyad is almost always in the range 60°–120°, in agreement with the perpendicular orientation in the re-refined X-ray structure. The noncoplanar arrangement is prevalent also in the β-secretase simulations, as well as in the runs with the inhibitor-bound proteases. Quantum-mechanics calculations provide further evidence that before catalysis the noncoplanar arrangement is favored energetically in eukaryotic aspartic proteases. Remarkably, the coplanar orientation of the catalytic dyad is observed in MD simulations of HIV-protease at 100 K but not at 300 K, which indicates that the noncoplanar arrangement is favored by conformational entropy. This finding suggests that the coplanar orientation in the crystal structures of apo aspartic proteases is promoted by the very low temperature used for data collection (usually around 100 K).

  • 13.
    Friedman, Ran
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Caflisch, Amedeo
    Department of Biochemistry, University of Zürich.
    Surfactant Effects on Amyloid Aggregation Kinetics2011In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 414, p. 303-312Article in journal (Refereed)
    Abstract [en]

    There is strong experimental evidence of the influence of surfactants (e.g., fatty acids) on the kinetics of amyloid fibril formation. However, the structures of mixed assemblies and interactions between surfactants and fibril-forming peptides are still not clear. Here, coarse-grained simulations are employed to study the aggregation kinetics of amyloidogenic peptides in the presence of amphiphilic lipids. The simulations show that the lower the fibril formation propensity of the peptides, the higher the influence of the surfactants on the peptide self-assembly kinetics. In particular, the lag phase of weakly aggregating peptides increases because of the formation of mixed oligomers, which are promoted by hydrophobic interactions and favorable entropy of mixing. A transient peak in the number of surfactants attached to the growing fibril is observed before reaching the mature fibril in some of the simulations. This peak originates from transient fibrillar defects consisting of exposed hydrophobic patches on the fibril surface, which provide a possible explanation for the temporary maximum of fluorescence observed sometimes in kinetic traces of the binding of small-molecule dyes to amyloid fibrils.

  • 14.
    Friedman, Ran
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences. University of Zürich, Switzerland.
    Caflisch, Amedeo
    University of Zürich, Switzerland.
    Wild type and mutants of the HET-s(218-289) prion show different flexibility at fibrillar ends: A simulation study2014In: Proteins: Structure, Function, and Bioinformatics, ISSN 0887-3585, E-ISSN 1097-0134, Vol. 82, no 3, p. 399-404Article in journal (Refereed)
    Abstract [en]

    The C-terminal segment (residues 218–289) of the HET-s protein of the filamentous fungus Podosporina anserina is a prion-forming domain. The structural model of the HET-s(218–289) amyloid fibril based on solid-state nuclear magnetic resonance (NMR) restraints shows a β solenoid topology which is comprised of a β-sheet core and interconnecting loops. For the single-point mutants Phe286Ala and Trp287Ala, slower aggregation rates in vitro and loss of prionic infectivity have been reported recently. Here we have used molecular dynamics to compare the flexibility of the mutants and wild type. The simulations, initiated from a trimeric aggregate extracted from the NMR structural model, show structural stability on a 100-ns time scale for wild type and mutants. Analysis of the fluctuations along the simulations reveals that the mutants are less flexible than the wild type in the C-terminal segment at only one of the two external monomers. Analysis of interaction energy and buried accessible surface indicates that residue Phe286 in particular is stabilized in the Trp287Ala mutant. The simulation results provide an atomistic explanation of the suggestion (based on indirect experimental evidence) that flexibility at the protofibril end(s) is required for fibril elongation. Moreover, they provide further evidence that the growth of the HET-s amyloid fibril is directional.

  • 15.
    Friedman, Ran
    et al.
    Tel Aviv University, Israel.
    Fischer, Stefan
    Nachliel, Esther
    Scheiner, Steve
    Gutman, Menachem
    Minimum energy pathways for proton transfer between adjacent sites exposed to water2007In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 21, p. 6059-6070Article in journal (Refereed)
    Abstract [en]

    The capacity to transfer protons between surface groups is an innate property of many proteins. The transfer of a proton between donor and acceptor, located as far as 6−7 Å apart, necessitates the participation of water molecules in the process. In a previous study we investigated the mechanism of proton transfer (PT) between bulk exposed sites, a few ångströms apart, using as a model the proton exchange between the proton-binding sites of the fluorescein molecule in dilute aqueous solution.1 The present study expands the understanding of PT reactions between adjacent sites exposed to water through the calculation the minimum energy pathways (MEPs) by the conjugate peak refinement algorithm2 and a quantum-mechanical potential. The PT reaction trajectories were calculated for the fluorescein system with an increasing number of water molecules. The MEP calculations reveal that the transition state is highly strained and involves a supramolecular structure in which fluorescein and the interconnecting water molecules are covalently bonded together and the protons are shared between neighboring oxygens. These findings are in accord with the high activation energy, as measured for the reaction, and indicate that PT reactions on the surface proceed by a semi- or fully concerted rather than stepwise mechanism. A similar mechanism is assumed to be operative on the surface of proteins and renders water-mediated PT reactions as highly efficient as they are.

  • 16.
    Friedman, Ran
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Khalid, Syma
    Univ Southampton, UK.
    Aponte-Santamaria, Camilo
    Univ Los Andes, Colombia;Heidelberg Univ, Germany.
    Arutyunova, Elena
    Univ Alberta, Canada.
    Becker, Marlon
    Univ Munster, Germany.
    Boyd, Kevin J.
    Univ Connecticut, USA.
    Christensen, Mikkel
    Aarhus Univ, Denmark;Sinodanish Ctr Educ & Res, Peoples Republic of China.
    Coimbra, Joao T. S.
    Univ Porto, Portugal.
    Concilio, Simona
    Univ Salerno, Italy.
    Daday, Csaba
    Heidelberg Inst Theoret Studies, Germany.
    van Eerden, Floris J.
    Univ Groningen, Netherlands.
    Fernandes, Pedro A.
    Univ Porto, Portugal.
    Graeter, Frauke
    Heidelberg Univ, Germany;Heidelberg Inst Theoret Studies, Germany.
    Hakobyan, Davit
    Univ Munster, Germany.
    Heuer, Andreas
    Univ Munster, Germany.
    Karathanou, Konstantina
    Free Univ Berlin, Germany.
    Keller, Fabian
    Univ Munster, Germany.
    Lemieux, M. Joanne
    Univ Alberta, Canada.
    Marrink, Siewert J.
    Univ Groningen, Netherlands.
    May, Eric R.
    Univ Connecticut, USA.
    Mazumdar, Antara
    Univ Groningen, Netherlands.
    Naftalin, Richard
    Kings Coll London, UK.
    Pickholz, Monica
    Univ Buenos Aires, Argentina.
    Piotto, Stefano
    Univ Salerno, Italy.
    Pohl, Peter
    Johannes Kepler Univ Linz, Austria.
    Quinn, Peter
    Kings Coll London, UK.
    Ramos, Maria J.
    Univ Porto, Portugal.
    Schiott, Birgit
    Aarhus Univ, Denmark.
    Sengupta, Durba
    Natl Chem Lab, India.
    Sessa, Lucia
    Univ Salerno, Italy.
    Vanni, Stefano
    Univ Fribourg, Switzerland.
    Zeppelin, Talia
    Aarhus Univ, Denmark.
    Zoni, Valeria
    Univ Fribourg, Switzerland.
    Bondar, Ana-Nicoleta
    Free Univ Berlin, Germany.
    Domene, Carmen
    Univ Bath, UK;Univ Oxford, UK.
    Understanding Conformational Dynamics of Complex Lipid Mixtures Relevant to Biology2018In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 251, no 5-6, p. 609-631Article, review/survey (Refereed)
    Abstract [en]

    This is a perspective article entitled "Frontiers in computational biophysics: understanding conformational dynamics of complex lipid mixtures relevant to biology" which is following a CECAM meeting with the same name.

  • 17.
    Friedman, Ran
    et al.
    University of Zürich, Switzerland.
    Pellarin, R
    Caflisch, A
    Amyloid aggregation on lipid bilayers and its impact on membrane permeability2009In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 387, no 2, p. 407-415Article in journal (Refereed)
  • 18.
    Friedman, Ran
    et al.
    University of Zürich, Switzerland.
    Pellarin, R
    Caflisch, A
    Soluble Protofibrils as Metastable Intermediates in Simulations of Amyloid Fibril Degradation Induced by Lipid Vesicles2010In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 1, no 2, p. 471-474Article in journal (Refereed)
  • 19.
    Georgoulia, Panagiota S.
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Todde, Guido
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Bjelic, Sinisa
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    The catalytic activity of Abl1 single and compound mutations: Implications for the mechanism of drug resistance mutations in chronic myeloid leukaemia2019In: Biochimica et Biophysica Acta - General Subjects, ISSN 0304-4165, E-ISSN 1872-8006, Vol. 1863, no 4, p. 732-741Article in journal (Refereed)
    Abstract [en]

    Background

    Abl1 is a protein tyrosine kinase whose aberrant activation due to mutations is the culprit of several cancers, most notably chronic myeloid leukaemia. Several Abl1 inhibitors are used as anti-cancer drugs. Unfortunately, drug resistance limits their effectiveness. The main cause for drug resistance is mutations in the kinase domain (KD) of Abl1 that evolve in patients. The T315I mutation confers resistance against all clinically-available inhibitors except ponatinib. Resistance to ponatinib can develop by compound (double) mutations.

    Methods

    Kinetic measurements of the KD of Abl1 and its mutants were carried out to examine their catalytic activity. Specifically, mutants that lead to drug resistance against ponatinib were considered. Molecular dynamics simulations and multiple sequence analysis were used for explanation of the experimental findings.

    Results

    The catalytic efficiency of the T315I pan-resistance mutant is more than two times lower than that of the native KD. All ponatinib resistant mutations restore the catalytic efficiency of the enzyme. Two of them (G250E/T315I and Y253H/E255V) have a catalytic efficiency that is more than five times that of the native KD.

    Conclusions

    The measurements and analysis suggest that resistance is at least partially due to the development of a highly efficient kinase through subsequent mutations. The simulations highlight modifications in two structurally important regions of Abl1, the activation and phosphate binding loops, upon mutations.

    General significance

    Experimental and computational methods were used together to explain how mutations in the kinase domain of Abl1 lead to resistance against the most advanced drug currently in use to treat chronic myeloid leukaemia.

  • 20.
    Karlsson, Björn C. G.
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Dilution of whisky - the molecular perspective2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, no 6489Article in journal (Refereed)
    Abstract [en]

    Whisky is distilled to around 70% alcohol by volume (vol-%) then diluted to about 40 vol-%, and often drunk after further slight dilution to enhance its taste. The taste of whisky is primarily associated with amphipathic molecules, such as guaiacol, but why and how dilution enhances the taste is not well understood. We carried out computer simulations of water-ethanol mixtures in the presence of guaiacol, providing atomistic details on the structure of the liquid mixture. We found that guaiacol is preferentially associated with ethanol, and, therefore, primarily found at the liquid-air interface in mixtures that contain up to 45 vol-% of ethanol. At ethanol concentrations of 59 vol-% or higher, guaiacol is increasingly surrounded by ethanol molecules and is driven to the bulk. This indicates that the taste of guaiacol in the whisky would be enhanced upon dilution prior to bottling. Our findings may apply to other flavour-giving amphipathic molecules and could contribute to optimising the production of spirits for desired tastes. Furthermore, it sheds light on the molecular structure of water-alcohol mixtures that contain small solutes, and reveals that interactions with the water may be negligible already at 89 vol-% of ethanol.

  • 21.
    Khrennikov, Andrei
    Växjö University, Faculty of Mathematics/Science/Technology, School of Mathematics and Systems Engineering. Matematik.
    Quantum equilibria for macroscopic systems2006In: Journal of Physics A: Mathematical and General, ISSN 0305-4470, Vol. 39, p. 8461-8475Article in journal (Refereed)
    Abstract [en]

    We found quantum equilibria for macroscopic systems.

  • 22. Mezer, A.
    et al.
    Friedman, Ran
    Tel Aviv University, Israel.
    Noivirt, O.
    Nachliel, E.
    Gutman, M.
    The mechanism of proton transfer between adjacent sites exposed to water2005In: J. Chem. Phys. B, Vol. 109, p. 11379-11388Article in journal (Refereed)
  • 23.
    Nicholls, Ian A.
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Andersson, Håkan S.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Golker, Kerstin
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Henschel, Henning
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Karlsson, Björn C. G.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Olsson, Gustaf D.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Rosengren, Annika M.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Shoravi, Siamak
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Wiklander, Jesper G.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Wikman, Susanne
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Rational Design of Biomimetic Molecularly Imprinted Materials: Theoretical and Computational Strategies for Guiding Nanoscale Structured Polymer Development2011In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 400, p. 1771-1786Article, review/survey (Refereed)
    Abstract [en]

    In principle, molecularly imprinted polymer science and technology provides a means for ready access to nano-structured polymeric materials of predetermined selectivity. The versatility of the technique has brought it to the attention of many working with the development of nanomaterials with biological or biomimetic properties for use as therapeutics or in medical devices. Nonetheless, the further evolution of the field necessitates the development of robust predictive tools capable of handling the complexity of molecular imprinting systems. The rapid growth in computer power and software over the past decade has opened new possibilities for simulating aspects of the complex molecular imprinting process. We present here a survey of the current status of the use of in silico-based approaches to aspects of molecular imprinting. Finally, we highlight areas where ongoing and future efforts should yield information critical to our understanding of the underlying mechanisms sufficient to permit the rational design of molecularly imprinted polymers.

  • 24.
    Nicholls, Ian A.
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Olsson, Gustaf D.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Karlsson, Björn C. G.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Suriyanarayanan, Subramanian
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Wiklander, Jesper G.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Theoretical and Computational Strategies in Molecularly Imprinted Polymer Development2018In: Molecularly Imprinted Polymers for Analytical Chemistry Applications / [ed] Wlodzimierz Kutner, Piyush Sindhu Sharma, London: Royal Society of Chemistry, 2018, p. 197-226Chapter in book (Refereed)
    Abstract [en]

    Theoretical and computational studies of molecular imprinting have helped provide valuable insights concerning the nature of the molecular-level events underlying the recognition characteristics of molecularly imprinted materials. Here, we first present an overview of a thermodynamic treatment of factors governing the behaviour of these functional materials, and then a summary of the development and current status of the use of computational strategies for studying aspects of molecular imprinting and the resulting material properties.

  • 25.
    Petersson, Tomas
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
    Hellsing, Bo
    Institutionen för fysik, Göteborgs Universitet.
    Detailed derivation of Gaussian orbital based matrix elements in electron structure calculations.2010In: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 31, p. 37-46Article in journal (Refereed)
    Abstract [en]

    A detailed derivation of analytic solutions is presented for overlap, kinetic, nuclear attraction and electron repulsion integrals involving Cartesian Gaussian-type orbitals. It is demonstrated how s-type orbitals can be used to evaluate integrals with higher angular momentum via the properties of Hermite polynomials and differentiation with respect to non-integration variables.

  • 26.
    Pineda De Castro, Luis Felipe
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Dopson, Mark
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Biological Membranes in Extreme Conditions: Anionic Tetraether Lipid Membranes and Their Interactions with Sodium and Potassium2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 41, p. 10628-10634Article in journal (Refereed)
    Abstract [en]

    Archaea such as Sulfolobus acidocaldarius tolerate extreme temperatures and high acidity and can grow in the presence of toxic metals and low concentrations of Na+ or K+. It is believed that their unique tetraether membranes protect them from harsh environments and allow their survival under such conditions. We used molecular dynamics simulations to study membranes comprising glycerol dialkylnonitol tetraether lipids, which are the main component of S. acidocaldariusmembranes, in solutions containing different concentrations of NaCl and KCl or with Na+ or K+counterions (trace cations, 0 M). Anionic binding sites on the membranes were almost 50% occupied in the presence of counterions. The free energy of cation–phosphate complexation and the residence times of ions near the membranes were found to be both ion- and concentration-dependent. Sodium ions had more favorable interactions with the membranes and a longer residence time, whereas higher cation concentrations led to shorter ion residence times. When only counterions were present in the solutions, large residence times suggested that the membrane may function as a cation-attracting reservoir. The results suggested that the ions can be easily transferred to the cytoplasm as needed, explaining the growth curves of S. acidocaldarius under different salinities and pH.

  • 27.
    Pineda De Castro, Luis Felipe
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences. University of Gdansk, Poland.
    Dopson, Mark
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Biological Membranes in Extreme Conditions: Simulations of Anionic Archaeal Tetraether Lipid Membranes2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 5, article id e0155287Article in journal (Refereed)
    Abstract [en]

    In contrast to the majority of organisms that have cells bound by di-ester phospholipids, archaeal membranes consist of di- and tetraether phospholipids. Originating from organisms that withstand harsh conditions (e.g., low pH and a wide range of temperatures) such membranes have physical properties that make them attractive materials for biological research and biotechnological applications. We developed force-field parameters based on the widely used Generalized Amber Force Field (GAFF) to enable the study of anionic tetraether membranes of the model archaean Sulfolobus acidocaldarius by computer simulations. The simulations reveal that the physical properties of these unique membranes depend on the number of cyclopentane rings included in each lipid unit, and on the size of cations that are used to ensure charge neutrality. This suggests that the biophysical properties of Sulfolobus acidocaldarius cells depend not only on the compositions of their membranes but also on the media in which they grow.

  • 28. Seeber, M
    et al.
    Felline, A
    Raimondi, F
    Muff, S
    Friedman, Ran
    Univ Zurich, Dept Biochem, CH-8057 Zurich, Switzerland .
    Rao, F
    Caflisch, A
    Fanelli, F
    Wordom: a user-friendly program for the analysis of molecular conformations, trajectories, and free energy surfaces2011In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 32, no 6, p. 1183-1194Article in journal (Refereed)
  • 29.
    Todde, Guido
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Activation and Inactivation of the FLT3 Kinase: Pathway Intermediates and the Free Energy of Transition2019In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 123, no 26, p. 5385-5394Article in journal (Refereed)
    Abstract [en]

    The aberrant expression of kinases is often associated with pathologies such as cancer and autoimmune diseases. Like other types of enzymes, kinases can adopt active and inactive states, where a shift toward more stable active state often leads to disease. Dozens of kinase inhibitors are, therefore, used as drugs. Most of these bind to either the inactive or active state. In this work, we study the transitions between these two states in FLT3, an important drug target in leukemias. Kinases are composed of two lobes (N- and C-terminal lobes) with the catalytic site in-between. Through projection of the largest motions obtained through molecular dynamics (MD) simulations, we show that each of the end-states (active or inactive) already possess the ability for transition as the two lobes rotate which initiates the transition. A targeted simulation approach known as essential dynamics sampling (EDS) was used to speed up the transition between the two protein states. Coupling the EDS to implicit-solvent MD was performed to estimate the free energy barriers of the transitions. The activation energies were found in good agreement with previous estimates obtained for other kinases. Finally, we identified FLT3 intermediates that assumed configurations that resemble that of the c-Src nonreceptor tyrosine kinase. The intermediates show better binding to the drug ponatinib than c-Src and the inactive state of FLT3. This suggests that targeting intermediate states can be used to explain the drug-binding patterns of kinases and for rational drug design.

  • 30.
    Todde, Guido
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Friedman, Ran
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Conformational modifications induced by internal tandem duplications on the FLT3 kinase and juxtamembrane domains2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 34, p. 18467-18476Article in journal (Refereed)
    Abstract [en]

    he aberrant expression of FLT3 tyrosine kinase is associated primarily with acute myeloid leukaemia. This blood malignancy is often related to the onset of internal tandem duplications (ITDs) in the native sequence of the protein. The ITDs occur mainly in the juxtamembrane domain of the protein and alter the normal activity of the enzyme. In this work, we have studied the native form of FLT3 and six mutants by molecular dynamics simulations. The catalytic activity of FLT3 is exerted by the tyrosine kinase domain (KD) and regulated by the juxtamembrane (JM) domain. Analysis of the dynamics of these two domains have shown that the introduction of ITDs in the JM domain alters both structural and dynamic parameters. The presence of ITDs allowed the protein to span a larger portion of the conformational space, particularly in the JM domain and the activation loop. The FLT3 mutants were found to adopt more stable configurations than the native enzyme. This was due to the different arrangements assumed by the JM domain. Larger fluctuations of the activation loop were found in four of the six mutants. In the native FLT3, the key residue Tyr(572) is involved in a strong and stable interaction with an ion pair. This interaction, which is thought to keep the JM in place hence regulating the activity of the enzyme, was found to break in all FLT3 mutants.

  • 31.
    Wiklander, Jesper G.
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Karlsson, Björn C. G.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Aastrup, Teodor
    Nicholls, Ian A.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Towards a synthetic avidin mimic2011In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 400, no 5, p. 1397-1404Article in journal (Refereed)
    Abstract [en]

    A series of streptavidin-mimicking molecularly imprinted polymers has been developed and evaluated for their biotin binding characteristics. A combination of molecular dynamics and NMR spectroscopy was used to examine potential polymer systems, in particular with the functional monomers methacrylic acid and 2-acrylamidopyridine. The synthesis of copolymers of ethylene dimethacrylate and one or both of these functional monomers was performed. A combination of radioligand binding studies and surface area analyses demonstrated the presence of selectivity in polymers prepared using methacrylic acid as the functional monomer. This was predicted by the molecular dynamics studies showing the power of this methodology as a prognostic tool for predicting the behavior of molecularly imprinted polymers.

  • 32.
    Åqvist, Johan
    et al.
    Uppsala University.
    Wennerström, Petra
    Uppsala University.
    Nervall, Martin
    Uppsala University.
    Bjelic, Sinisa
    Uppsala University.
    Brandsdal, Bjørn O.
    Uppsala University.
    Molecular dynamics simulations of water and biomolecules wit a Monte Carlo constant pressure algorithm2004In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 384, no 4-6, p. 288-294Article in journal (Refereed)
    Abstract [en]

    A mixed molecular dynamics/Monte Carlo (MD/MC) algorithm for constant pressure simulations of arbitrary molecular systems is examined. Calculations are reported at ambient and high pressures both for liquid water systems and for a chemical reaction step in a solvated enzyme utilizing empirical valence bond potentials. The present method reproduces earlier reported results well and is computationally efficient since it does not require the virial to be evaluated at each MD step. It is also found that the effects of introducing MC volume steps on the dynamics of the system are negligible provided that the volume step sizes and updating frequencies are appropriately chosen.

1 - 32 of 32
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