Salt-bridge interactions between acidic and basic amino acids contribute to the structural stability of proteins and to protein-protein interactions. A conserved salt-bridge is a canonical feature of the alpha-defensin antimicrobial peptide family, but the role of this common structural element has not been fully elucidated. We have investigated mouse Paneth cell alpha-defensin cryptdin-4 (Crp4) and peptide variants with mutations at Arg(7) or Glu(15) residue positions to disrupt the salt-bridge and assess the consequences on Crp4 structure, function, and stability. NMR analyses showed that both (R7G)-Crp4 and (E15G)-Crp4 adopt native-like structures, evidence of fold plasticity that allows peptides to reshuffle side chains and stabilize the structure in the absence of the salt-bridge. In contrast, introduction of a large hydrophobic side chain at position 15, as in (E15L)-Crp4 cannot be accommodated in the context of the Crp4 primary structure. Regardless of which side of the salt-bridge was mutated, salt-bridge variants retained bactericidal peptide activity with differential microbicidal effects against certain bacterial cell targets, confirming that the salt-bridge does not determine bactericidal activity per se. The increased structural flexibility induced by salt-bridge disruption enhanced peptide sensitivity to proteolysis. Although sensitivity to proteolysis by MMP7 was unaffected by most Arg(7) and Glu(15) substitutions, every salt-bridge variant was degraded extensively by trypsin. Moreover, the salt-bridge facilitates adoption of the characteristic alpha-defensin fold as shown by the impaired in vitro refolding of (E15D)-proCrp4, the most conservative salt-bridge disrupting replacement. In Crp4, therefore, the canonical alpha-defensin salt-bridge facilitates adoption of the characteristic alpha-defensin fold, which decreases structural flexibility and confers resistance to degradation by proteinases.

The marine ribbon worms (nemerteans) are predators which capture their prey by everting a proboscis carrying a mixture of toxins which brings on rapid paralysis [1]. Moreover, ribbon worms have a thick layer of epidermal mucus of similar constitution. Tetrodotoxin (TTX) has been identified as one of these toxins [2]. The extreme toxicity of TTX (lethal by ingestion of 0.5-2 mg) is due to its ability to block voltage-gated sodium channels. Although several bacterial species (among these Vibrio sp.) have been linked to its synthesis, the biogenic origin and biosynthesis is unclear. One hypothesis is that TTX production occurs in a symbiotic relationship with its host, in this case the ribbon worm [3]. We have made significant effort to identify TTX in a setup for production through the cultivation of Vibrio alginolyticus in nutrient broth infused with mucus from the ribbon worm Lineus longissimus. Toxicity was demonstrated by fraction injections into shore crabs, but no TTX was found, and it could be shown conclusively that toxicity was unrelated to TTX and the Vibrio culture itself, and rather a constituent of the ribbon worm mucus [4]. The following studies led us to the discovery of a new class of peptides, the alpha-nemertides, in the mucus of the ribbon worms, which could be directly linked to the toxic effects. A literature review of the available evidence for TTX in ribbon worms show that the evidence in most cases are indirect, although notable exceptions exist. This points to the necessity to further investigate the presence and roles of TTX and alpha-nemertides in ribbon worms.

We recently discovered a novel family of neuroactive peptides in nemerteans, which we have named alpha-nemertides (1). One of these peptides, nemertide alpha-1, has been the subject of detailed studies with regard to structure and effects. The peptide exhibits exceptional potency against a number of arthropod species. Moreover, in vitro experiments suggest that alpha-1 acts primarily on voltage-gated sodium channels, and that this action is selective for arthropods by two orders of magnitude over vertebrate species. Using transcriptomic and proteomic approaches, we have identified 10 alpha-nemertides, but this number is likely to increase. These peptides alongside with a series of mutants are currently under evaluation by our group, with the goal to improve our understanding of structure-function relationships. In addition, we are considering potential practical uses of alpha-nemertides. In this talk, I will describe the current status of this research project.

1. E. Jacobsson et al., Peptide ion channel toxins from the bootlace worm, the longest animal on Earth. Scientific reports 8, 4596 (2018).

Ribbon worms (nemerteans) are marine predators, which capture their prey using a proboscis containing a mixture of toxins which brings on rapid paralysis [1]. In addition, their epidermis contains thick mucus of similar toxic constitution. One very potent toxin reported in ribbon worm mucus is tetrodotoxin (TTX). However, despite significant efforts, Strand et al. [2] were unable to detect any TTX, neither in the mucus of the ribbon worm Lineus longissimus, nor from Vibrio alginolyticus cultures isolated from and cultivated in the mucus. These observations challenged the notion of general presence of TTX in ribbon worm mucus, and prompted us to look for other toxins [3]. Using LC-MS analysis of mucus extracts, we identified three peptides present in significant amounts. The peptides were sequenced using a combination of MS/MS analysis and transcriptomics, and whereas one of them strongly resembles the only peptide toxin previously characterized from ribbon worms, Neurotoxin B-IV [4], the other two were found to represent a previously unknown class of peptide toxins. The most abundant of these was synthesized, and its 3D structure determined. Preliminary toxicity tests on shore crab (C. maenas) indicated toxicity (through paralysis) on par with that of TTX. Further analyses have indicated that its toxic effects are due to binding to voltage sensitive sodium channels.

With L. longissimus as our primary target, we are now mapping the presence of peptide toxins in ribbon worms, with the objectives to establish routes for synthesis, and to characterize the biological activities and structures of these peptides. The number of peptides of this novel class is increasing, and synthesis and characterization is well underway. The striking potencies of these peptides make them potentially amenable as novel insecticidal or anthelmintic leads, pharmacological tools or in biotechnology applications.

References

1. Strand M, Sundberg P. Nationalnyckeln till Sveriges flora och fauna [DO-DP]. Stjärnmaskar-Slemmaskar: Sipuncula-Nemertea: Artdatabanken, SLU; 2010.

2. Strand M, Hedstrom M, Seth H, McEvoy EG, Jacobsson E, Goransson U, Andersson HS, Sundberg P. The Bacterial (Vibrio alginolyticus) Production of Tetrodotoxin in the Ribbon Worm Lineus longissimus-Just a False Positive? Marine Drugs. 2016;14(4).

3. Strand M, Andersson HS. Slemmaskens hemlighet. Forskning & Framsteg. 2016;(2):26-33.

4. Blumenthal KM, Kem WR. Structure and action of heteronemertine polypeptide toxins. Primary structure of Cerebratulus lacteus toxin B-IV. The Journal of Biological Chemistry. 1976;251(19):6025-9.

Earlier studies have implied a change in dietary habits of the Swedish population towards a low carbohydrate, high fat diet. Questions have been raised about the development in recent years and potential health effects. We have investigated the dietary intake of Swedish female students enrolled in a university nutrition course between 2002 and 2017. The students carried out self-reporting of all food and drink intake over one weekday and one weekend day. Intake of macronutrients (E%) and micronutrients were calculated for the whole period while statistical analysis was performed for changes between 2009 and 2017 (729 women). Results showed significant changes in carbohydrate intake (from 47.0 to 41.4 E%) and fat intake (from 31.7 to 37.5 E%). Carbohydrate intake was significantly lower than the Nordic Nutrition Recommendations (45-60 E%). However, daily fiber intake remains high (3.0 g/MJ) in a national context, and intake of vitamin D and folate appears to increase during the period. The results suggest that the observed national transition from carbohydrate to fat intake persists, and that it might be especially evident among individuals interested in food and nutrition. Considering the fiber and micronutrient intake, the change is not necessarily unfavorable for this particular group.

While the Swedish nutrition recommendations have been kept relatively constant in recent years, public attitudes to different diets have been swinging faster. The National food survey (Riksmaten), being performed in Sweden only once per decade, cannot identify any corresponding rapid changes in diets. Hence, our understanding of potential fluctuations is limited. During the last 15 years, nutrition students at the Linnaeus University (formerly University of Kalmar) have reported their food intake in the context of the course Diet, Nutrition and Health 7,5 hp. The result is an extensive data set comprising more than 1100 individuals and over 2500 days of food intake reports, and although not originally intended or designed as a study, it became apparent that these data could be of interest as an indicator for national dietary trends. Food intake was reported (by weighing or estimating the amounts) for two weekdays and one weekend day per student, along with age, length, sex and weight. Food intake was translated to nutrient intake using Dietist Net software (Kost & Näringsdata).  Admittedly, the data set has some validity problems: the students differ from the Riksmaten study groups in mean age and geographical distribution, and all data was collected during March-April. As students in a nutrition course, they can also be expected to be more interested and more knowledgeable in the nutrition subject than the average person. Nevertheless, the results clearly demonstrate a substantial change in nutrient intake from 2006 and onwards, where the energy from carbohydrates decreased from above 50% to below 40%, and where the energy intake from fat increased from about 25% to 36%. Further details, such as the effects on the intake of selected micronutrients, will be presented.

Most ribbon worms (phylum: Nemertea) are found in marine environments, where they act as predators and scavengers. They are characterized by an eversible proboscis that is used to hunt for prey and thick mucus covering their skin. Both proboscis and epidermal mucus mediate toxicity to predators and preys. Research into the chemical nature of the substances that render toxicity has not been extensive, but it has nevertheless led to the identification of several compounds of potential medicinal use or for application in biotechnology. This review provides a complete account of the current status of research into nemertean toxins.

Defensins are multifunctional antimicrobial peptides expressed in several tissue types and leucocytes as part of the innate immune response against microbes. Based on the three-dimensional structure and disulfide connectivity, vertebrate defensins are subdivided into α-, β-, and θ-defensins. While all three types have been found in mammals, only β-defensins have been identified in birds. Genetic studies have revealed dozens of different avian β-defensin (AvBD) genes in different bird species, as well as allelic variation for different genes. Knowledge of the relation between avian peptide structure features and antimicrobial activity is however limited. In this study, the structure-functional relations of three variants of AvBD3b, a mallard (Anas platyrhynchos) defensin of evolutionary interest, was investigated. Gene alleles encoding two of these peptides, AvBD3b:1 and AvBD3b:2 are common in mallards, whereas AvBD3b:3 occurs rare. These β-defensin peptides were synthesized as linear peptides and subjected to oxidative folding. The three-dimensional structure of AvBD3b:1, including disulfide bond connectivity, was determined using NMR, and those of AvBD3b:2 and AvBD3b:3 respectively, were modelled using AvBD3b:1 as the template. The antimicrobial activities of folded peptides were compared to those of linear peptides. The NMR analysis showed that folded AvBD3b adopts a three-dimensional structure typical for β-defensins, including C-terminal antiparallel β-sheets and disulfide bond organization between six cysteine (C) residues: C6-C34, C13-C28, and C18-C35. Analyses of antimicrobial activity showed that both folded and linear variants of the three peptides inhibited bacterial growth. However, differences in activity were observed, suggesting that folded AvBD3b:3 was the most efficient against both Gram-negative and Gram-positive bacteria. Taken together, these findings provide additional insight into the influence of amino acid sequence variation and three-dimensional structure on the antimicrobial activity of mallard AvBD3b.

Avian β-defensins are an important class of antimicrobial peptides in birds. These short cationic peptides are directly involved in the clearance of infections by membrane disruption, but can also act as immunomodulators and chemotactic agents recruiting immune cells. Recent genomic studies have shown the presence of several different avian β-defensin (AvBD) genes across the avian phylogeny, but also significant copy number variation and occurrence of pseudogenes. In mallard (Anas platyrhynchos) and other waterfowl AvBD genes are conserved and seem to be maintained by purifying selection. Due to their relatively simple peptide structure and direct mode of action, AvBDs is a potential tractable system to investigate how small differences in the gene sequence translates into differences in immune function. Here, we used genomic information from three different mallard defensin loci (AvBD4, AvBD10 and AvBD13) and synthesized the linear peptides from the most common allele of each locus, plus two rare alleles from AvBD13 locus and measured their antimicrobial activity against Gram-negative (E. coli and S. Typhimurium) and Gram-positive (S. aureus and M. luteus) bacteria. In these assays, AvBD4 showed the most potent antibacterial activity against both Gram-negative and Gram-positive bacteria, with an IC50 value of 0.48 mM against S. Typhimurium. Among AvBD13 peptides, the less frequently observed AvBD13:2 variant, was most potent, with IC50 value against S. aureus approximately 15 times lower than that of the most common AvBD13:1. Interestingly, AvBD10 had no antibacterial effect on the tested bacteria. Thus, antimicrobial function varied substantially among loci, but also within the AvBD13 locus, suggesting a direct link between genetic variation and immune function variation. Interestingly, results from assays with AvBD4 and AvBD13 seem to indicate that a higher positive net charge in peptides is associated with a more potent antibacterial effect.

Previous studies have demonstrated a correlation between diet cost and adherence to nutritional recommendations among consumers in general. This has adverse effects on diet and health inequality. It could be hypothesized that consumers knowledgeable in nutrition escape this correlation

Polypeptides from animal venoms have found important uses as drugs, pharmacological tools, and within biotechnological and agricultural applications. We here report a novel family of cystine knot peptides from nemertean worms, with potent activity on voltage-gated sodium channels. These toxins, named the alpha-nemertides, were discovered in the epidermal mucus of Lineus longissimus, the 'bootlace worm' known as the longest animal on earth. The most abundant peptide, the 31-residue long alpha-1, was isolated, synthesized, and its 3D NMR structure determined. Transcriptome analysis including 17 species revealed eight alpha-nemertides, mainly distributed in the genus Lineus. alpha-1 caused paralysis and death in green crabs (Carcinus maenas) at 1 mu g/kg (similar to 300 pmol/kg). It showed profound effect on invertebrate voltage-gated sodium channels (e.g. Blattella germanica Na(v)1) at low nanomolar concentrations. Strong selectivity for insect over human sodium channels indicates that a-nemertides can be promising candidates for development of bioinsecticidal agents.

Världens längsta djur, slemmasken långsnöre, producerar nervgifter som kan döda både krabbor och kackerlackor.

The further evolution of molecularly imprinted polymer science and technology necessitates the development of robust predictive tools capable of handling the complexity of molecular imprinting systems. A combination of the rapid growth in computer power over the past decade and significant software developments have 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. 

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.