1.C.17 The Cecropin (Cecropin) Family
Many organisms synthesize proteins (or peptides) which are degraded to relatively small hydrophobic or amphipathic, bioactive peptides. These peptides exhibit antibiotic, fungicidal, virucidal, hemolytic and/or tumoricidal activities by interacting with membranes and forming transmembrane channels that allow the free flow of electrolytes, metabolites and water across the phospholipid bilayers. Most of these peptides appear to function in biological warfare. There are many designations given to these bioactive peptides. They include the magainins, cecropins, melittins, defensins, bacteriocidins, etc. The proteins in each family within this functional superfamily are homologous, but they exhibit little or no significant sequence similarity with members of the other families. Thus, each family may have evolved independently. However, certain common structural features observed between members of distinct families suggest that at least some of these families share a common ancestry.
The generalized transport reaction catalyzed by channel-forming amphipathic peptides is:
small solutes, electrolytes and water (in) small solutes, electrolytes and water (out).
Several families of eukaryotic channel-forming amphipathic peptide, each from a different group of organisms, are recognized. Other non-insect derived cecropin-like peptides are members of the Cecropin superfamily.
Cecropins are produced by insects, particularly under conditions of infection. Cecropins A, B and D are close homologues consisting of 35-39 residues. They are found in the pupae of the cecropin moth, but related homologues named lepodopteran, bactericidin, moricin and sarcotoxin are produced by other insects.