Immune challenge to the insect Podisus maculiventris induces synthesis of a 21-residue peptide with sequence homology to frog skin antimicrobial peptides of the brevinin family. The insect and frog peptides have in common a C-terminally located disulfide bridge delineating a cationic loop. The peptide is bactericidal and fungicidal, exhibiting the largest antimicrobial spectrum observed so far for an insect defense peptide. An all-D-enantiomer is nearly inactive against Gram-negative bacteria and some Gram-positive strains but is fully active against fungi and other Gram-positive bacteria, suggesting that more than one mechanism accounts for the antimicrobial activity of this peptide. Studies with truncated synthetic isoforms underline the role of the C-terminal loop and flanking residues for the activity of this molecule for which we propose the name thanatin.
We have isolated from the blood of immune-challenged and untreated mussels (Mytilus edulis) antibacterial and antifungal peptides. We have characterized two isoforms of a novel 34-residue, cysteine-rich, peptide with potent bactericidal activity and partially characterized a novel 6.2-kDa antifungal peptide containing 12 cysteines. We report the presence of two members of the insect defensin family of antibacterial peptides and provide a phylogenetic analysis that indicates that mollusc and arthropod defensins have a common ancestry. Our data argue that circulating antimicrobial peptides represent an ancient host defense mechanism that predated the separation between molluscs and arthropods at the root of the Cambrian, about 545 million years ago.The antimicrobial defense of molluscs has attracted surprisingly little attention in view of the economic interest of many representatives of this phylum. Although generally considered to be capable of mounting an efficient host defense, molluscs are obviously susceptible to several microbial pathogens, as illustrated by the frequent waves of lethal diseases affecting populations of oysters and mussels, for instance. The current view holds that molluscs rely predominantly on cellular defense reactions in which invading microorganisms are either phagocytosed or encapsulated by blood cells or lymph cells. The presence of macromolecules with antimicrobial activity has been reported from the mucus of the giant snail Achatina fulica (the 150-kDa achacin; Refs. 1-3) and from egg mass and purple fluid of the sea hare, Aplysia kurodai (4, 5). Remarkably though, molluscs had not been reported, to date, to contain in their blood antimicrobial peptides to fight off bacteria and fungi. Such molecules are one of the hallmarks of the antimicrobial host defense of arthropods (for review, see Refs. 6 and 7), and they play a significant role in the survival against invading bacteria and fungi in higher insects, as illustrated recently for Drosophila (8). It was unclear whether the absence of any report on such molecules in molluscs reflected the lack of, or inaccurate, research in this field, or whether indeed molluscs had developed basically different strategies for their antimicrobial defense.We were intrigued by this situation, and in the course of a broad range phylogenetic study on the antimicrobial peptides in invertebrates, one of us (S. C.) collected specimens of the lamellibranch Mytilus edulis at the Zoological Outstation of the St. Petersburg University on the White Sea. Applying the same methodologies that we have used for isolating antimicrobial peptides from insects, we were able to detect in the blood of control and bacteria-challenged mussels the presence of several antibacterial and antifungal peptides. We report here the characterization of two types of small sized, cationic, cysteine-rich peptides; one of these, which we name mytilin, is a 34-residue, novel peptide with potent bactericidal activity. The other is clearly a member of the large family of 35-43-residue, c...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.