Selective reciprocity in antimicrobial activity versus cytotoxicity of hBD-2 and crotamine

Recent discoveries suggest cysteine-stabilized toxins and antimicrobial peptides have structure-activity parallels derived by common ancestry. Here, human antimicrobial peptide hBD-2 and rattlesnake venom-toxin crotamine were compared in phylogeny, 3D structure, target cell specificity, and mechanisms of action. Results indicate a striking degree of structural and phylogenetic congruence. Importantly, these polypeptides also exhibited functional reciprocity: (i) they exerted highly similar antimicrobial pH optima and spectra; (ii) both altered membrane potential consistent with ion channel-perturbing activities; and (iii) both peptides induced phosphatidylserine accessibility in eukaryotic cells. However, the Nav channel-inhibitor tetrodotoxin antagonized hBD-2 mechanisms, but not those of crotamine. As crotamine targets eukaryotic ion channels, computational docking was used to compare hBD-2 versus crotamine interactions with prototypic bacterial, fungal, or mammalian K-v channels. Models support direct interactions of each peptide with K-v channels. However, while crotamine localized to occlude K-v channels in eukaryotic but not prokaryotic cells, hBD-2 interacted with prokaryotic and eukaryotic K-v channels but did not occlude either. Together, these results support the hypothesis that antimicrobial and cytotoxic polypeptides have ancestral structure-function homology, but evolved to preferentially target respective microbial versus mammalian ion channels via residue-specific interactions. These insights may accelerate development of anti-infective or therapeutic peptides that selectively target microbial or abnormal host cells.