Structure Elucidation and Functional Studies of a Novel β-hairpin Antimicrobial Peptide from the Marine Polychaeta Capitella teleta

Endogenous antimicrobial peptides (AMPs) are evolutionary ancient molecular factors of innate immunity that play a key role in host defense. Among the most active and stable under physiological conditions AMPs are the peptides of animal origin that adopt a β-hairpin conformation stabilized by disulfide bridges. In this study, a novel BRICHOS-domain related AMP from the marine polychaeta Capitella teleta, named capitellacin, was produced as the recombinant analogue and investigated. The mature capitellacin exhibits high homology with the known β-hairpin AMP family—tachyplesins and polyphemusins from the horseshoe crabs. The β-hairpin structure of the recombinant capitellacin was proved by CD and NMR spectroscopy. In aqueous solution the peptide exists as monomeric right-handed twisted β-hairpin and its structure does not reveal significant amphipathicity. Moreover, the peptide retains this conformation in membrane environment and incorporates into lipid bilayer. Capitellacin exhibits a strong antimicrobial activity in vitro against a wide panel of bacteria including extensively drug-resistant strains. In contrast to other known β-hairpin AMPs, this peptide acts apparently via non-lytic mechanism at concentrations inhibiting bacterial growth. The molecular mechanism of the peptide antimicrobial action does not seem to be related to the inhibition of bacterial translation therefore other molecular targets may be assumed. The reduced cytotoxicity against human cells and high antibacterial cell selectivity as compared to tachyplesin-1 make it an attractive candidate compound for an anti-infective drug design.     

Mechanism of Action and Therapeutic Potential of the β-Hairpin Antimicrobial Peptide Capitellacin from the Marine Polychaeta Capitella teleta

Among the most potent and proteolytically resistant antimicrobial peptides (AMPs) of animal origin are molecules forming a β-hairpin structure stabilized by disulfide bonds. In this study, we investigated the mechanism of action and therapeutic potential of the β-hairpin AMP from the marine polychaeta Capitella teleta, named capitellacin. The peptide exhibits a low cytotoxicity toward mammalian cells and a pronounced activity against a wide range of bacterial pathogens including multi-resistant bacteria, but the mechanism of its antibacterial action is still obscure. In view of this, we obtained analogs of capitellacin and tachyplesin-inspired chimeric variants to identify amino acid residues important for biological activities. A low hydrophobicity of the β-turn region in capitellacin determines its modest membranotropic activity and slow membrane permeabilization. Electrochemical measurements in planar lipid bilayers mimicking the E. coli membrane were consistent with the detergent-like mechanism of action rather than with binding to a specific molecular target in the cell. The peptide did not induce bacterial resistance after a 21-day selection experiment, which also pointed at a membranotropic mechanism of action. We also found that capitellacin can both prevent E. coli biofilm formation and destroy preformed mature biofilms. The marked antibacterial and antibiofilm activity of capitellacin along with its moderate adverse effects on mammalian cells make this peptide a promising scaffold for the development of drugs for the treatment of chronic E. coli infections, in particular those caused by the formation of biofilms.     

Mitochondrial DNA D‐loop haplogroup contributions to the genetic diversity of East European domestic chickens from Russia

To elucidate geographical and historical aspects of chicken dispersal across Eastern Europe, we analysed the complete mitochondrial DNA D‐loop sequence of 86 representatives from chicken breeds traditionally raised in the territory of the East European Plain (Orloff, Pavlov, Russian White, Yurlov Crower, Uzbek Game and Naked Neck). From the 1231–1232 bp D‐loop sequence, 35 variable sites that defined 22 haplotypes were identified in modern chicken. All populations, except Uzbek Game, exhibited high values of haplotype and nucleotide diversity suggesting a wide variation in maternal diversity. Inclusion of mtDNA sequences from other European and Asian countries revealed representatives from this study belonging to haplogroups A, E1 and C1. We also assessed fossil chicken material dated to the 9th–18th century from archaeological sites in Northern and Eastern Europe. Three haplotypes found in the fossil specimens belonged to haplogroup E1, while one sample dated to the 18th century was assigned to the C1 haplogroup. This is the first report of the occurrence of the C1 haplogroup in European chicken populations prior to the 20th century based on the fossil material. These results provide evidence for a relatively recent introduction of all haplotypes other than E1 into the East European chicken gene pool with the significant impact of the C1 haplogroup mainly distributed in Southern China.     

Observations on larval fish transport and retention on the Scotian Shelf in relation to geostrophic circulation

We draw inferences about the dynamic processes responsible for the dispersal of ichthyoplankton on small marine banks using physical and biological data derived from static point-estimates of water-mass characteristics and ichthyoplankton collected concomitantly on the central Scotian Shelf. Where the density field evolves slowly and ageostrophic forcing is weak, the near-surface geostrophic flow can be derived from hydrographic data using the dynamic height method modified for shallow seas. We assess our interpretations of larval distributions using simple particle tracking. The hydrography of the Scotian Shelf during November of 1997 was typical of late autumn, when density is determined by surface variation in salinity. Surface isopycnals generally paralleled isobaths, and there was no evidence of strong surface fronts. Sizes of larvae of pelagic origin (e.g. cod and hake) on Western Bank (sole spawning source) increased and became skewed towards larger animals (cod, 3–10 mm; hake, 5–15 mm) in water-mass (Temperature and Salinity) space along isopycnals, consistent with gradual mixing and limited transport in the geostrophic flow (i.e. retention). Conversely, larvae of benthic origin (e.g. herring, 6–25 mm) were distributed across water-mass space, consistent with multiple origins and substantial transport. Our results indicate that dispersal from small, low-energy marine banks results from the interaction of spawning location, geostrophic currents and bathymetric steering, and requires neither convergence nor larval behaviour.