Diversity of the penaeidin antimicrobial peptides in two shrimp species

Penaeidins, a unique family of antimicrobial peptides (AMPs) with both proline and cysteine-rich domains, were initially identified in the hemolymph of the Pacific white shrimp, Litopenaeus vannamei. Described here are the results of an investigation of penaeidin diversity in individual shrimp from two species, L. vannamei and L. setiferus (Atlantic white shrimp). We report the discovery of a novel penaeidin class, designated penaeidin 4 present in both L. vannamei and L. setiferus, and that all penaeidin classes were expressed in a single individual. In addition, nearly all penaeidins, regardless of class, shared an identical leader sequence while differing dramatically in the remainder of the peptide. Several new class 3 isoforms were identified, as well as sequence variants of Lnu3a, which differ in the 3' untranslated region. Penaeidin sequence variability (especially of class 3), within and between individuals, is not interpretable as simple allelic polymorphism and may reflect alternate transcriptional mechanisms. Penaeidins are encoded by a small number of genetic loci and are not likely representatives of a large gene family produced by whole gene duplication, but rather may be products of a multi-component locus. Based on phylogenetic analysis, penaeidins fall into three classes where 1 and 2 are combined while classes 3 and 4 remain distinct. Phylogenetic analysis indicates that all classes of penaeidin were likely present in both species prior to speciation.