Crustins, Homologues of an 11.5-kDa Antibacterial Peptide, from Two Species of Penaeid Shrimp, Litopenaeus vannamei and Litopenaeus setiferus

The response of crustaceans to pathogens is believed to depend solely on innate, nonadaptive immune mechanisms, including phagocytosis, encapsulation, clotting, and a variety of soluble antimicrobial activities. Arthropod antimicrobial peptides, while characterized primarily from insects, also have been isolated from crustaceans. Expressed sequence tag analysis of hemocyte complementary DNA libraries from 2 species of shrimp, Litopenaeus vannamei and Litopenaeus setiferus, revealed transcripts with strong sequence similarity to an 11.5-kDa antibacterial peptide (crustin Cm1) found in Carcinus maenas. Crustins were also observed to contain motifs common to proteinase inhibitors. Analysis of these cDNA libraries yielded at least 3 different isoforms of this peptide in L. vannamei (crustin Lv1–Lv3) and 3 in L. setiferus (crustin Ls1–Ls3). Further analysis of a second L. vannamei cDNA library revealed the presence of 3 more possible isoforms (crustin Lv4–Lv6), which differed from those seen in the first L. vannamei cDNA library. Genomic Southern blot analysis revealed a complex family of crustin-related sequences. However, full-length crustin appears to be encoded by a much more restricted subset of sequences within this family.