cDNA cloning of three cecropin‐like antimicrobial peptides (Styelins) from the tunicate, Styela clava

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Abstract
We cloned precursors of three new antimicrobial peptides, Styelins C, D and E, from a pharyngeal cDNA library of a tunicate, Styela clava. Preprostyelins resembled dipteran preprocecropins, while the mature domain of Styelin C resembled Cecropin P1, an antimicrobial peptide purified from the porcine intestine. Beginning with the last 6 residues of their signal sequences, Styelin C and Cecropin 1 from Drosophila virilis had 8/11 identical amino acids (72.7%). Moreover, 4 of the last 6 residues of their mature peptide domains were also identical. Styelins were shorter, by 8 residues, than dipteran cecropins and preprostyelins contained a conserved, polyanionic C‐terminal extension that was absent in preprocecropins. Delineation of cecropin‐like antimicrobial peptides in a protochordate supports the antiquity of this family as effectors of innate immunity in animals and it increases the likelihood that additional cecropin‐like peptides will be found among other evolutionary descendants of protochordates — vertebrates.