The noncolligative peptide and glycopeptide antifreezes found in some cold-water fish act by binding to the ice surface and preventing crystal growth, not by altering the equilibrium freezing point of the water. A simple crystal growth and etching technique allows determination of the crystallographic planes where the binding occurs. In the case of elongated molecules, such as the alpha-helical peptides in this report, it also allows a deduction of the molecular alignment on the ice surface. The structurally similar antifreeze peptides from winter flounder (Pseudopleuronectes americanus) and Alaskan plaice (Pleuronectes quadritaberulatus) adsorb onto the (2021) pyramidal planes of ice, whereas the sculpin (Myoxocephalus scorpius) peptide adsorbs on (2110), the secondary prism planes. All three are probably aligned along (0112). These antifreeze peptides have 11-amino acid sequence repeats ending with a polar residue, and each repeat constitutes a distance of 16.5 A along the helix, which nearly matches the 16.7 A repeat spacing along (0112) in ice. This structural match is undoubtedly important, but the mechanism of binding is not yet clear. The suggested mechanism of growth inhibition operates through the influence of local surface curvature upon melting point and results in complete inhibition of the crystal growth even though individual antifreeze molecules bind at only one interface orientation.

No abstract

No abstract

Hepcidin is a small bioactive peptide with dual roles as an antimicrobial peptide and as the principal hormonal regulator of iron homeostasis in human and mouse. Hepcidin homologs of very similar structures are found in lower vertebrates, all comprise approximately 20-25 amino acids with 8 highly conserved cysteines forming 4 intramolecular disulfide bonds, giving hepcidin a hairpin structure. Hepcidins are particularly diverse in teleost fishes, which may be related to the diversity of aquatic environments with varying degree of pathogen challenge, oxygenation, and iron concentration, factors known to alter hepcidin expression in mammals. We characterized the diversity of hepcidin genes of the Antarctic notothenioid fishes that are endemic to the world's coldest and most oxygen-rich marine water. Notothenioid fishes have at least 4 hepcidin variants, in 2 distinctive structural types. Type I hepcidins comprise 3 distinct variants that are homologs of the widespread 8-cysteine hepcidins. Type II is a novel 4-cysteine variant and therefore only 2 possible disulfide bonds, highly expressed in hematopoietic tissues. Analyses of d(N)/d(S) substitution rate ratios and likelihood ratio test under site-specific models detected significant signal of positive Darwinian selection on the mature hepcidin-coding sequence, suggesting adaptive evolution of notothenioid hepcidins. Genomic polymerase chain reaction and Southern hybridization showed that the novel type II hepcidin occurs exclusively in lineages of the Antarctic notothenioid radiation but not in the basal non-Antarctic taxa, and lineage-specific positive selection was detected on the branch leading to the type II hepcidin clade under branch-site models, suggesting adaptive evolution of the reduced cysteine variant in response to the polar environment. We also isolated a structurally distinct 4-cysteine (4cys) hepcidin from an Antarctic eelpout that is unrelated to the notothenioids but inhabits the same freezing water. Neighbor-Joining (NJ) analyses of teleost hepcidins showed that the eelpout 4cys variant arose independently from the notothenioid version, which lends support to adaptive evolution of reduced cysteine hepcidin variants on cold selection. The NJ tree also showed taxonomic-specific expansions of hepcidin variants, indicating that duplication and diversification of hepcidin genes play important roles in evolutionary response to diverse ecological conditions.