Molecular identification and characterization of Type I crustin isoforms from the hemocytes of portunid crabs, Scylla tranquebarica and Portunus pelagicus

Crustins are cationic antimicrobial peptides of ca. 7–14 kDa with a characteristic four-disulphide core containing WAP domain, present in the hemocytes of crustaceans. The present study reports the first crustin sequences from two portunid crabs, viz. the mud crab Scylla tranquebarica (St-Crustin, JQ965930) and the blue swimmer crab Portunus pelagicus (Pp-Crustin, JQ753312). St-Crustin and Pp-Crustin represented the complete cDNA sequence of Type I crustin, with an ORF of 336 bp encoding 111 aa with a predicted molecular weight of 10 kDa and a pI of 8. The signal sequence contained 21 aa residues, which was followed by a mature peptide with a WAP domain at the C-terminus. Peptide model of St-Crustin and Pp-Crustin indicated a randomly coiled structure enclosing two β-sheets but no helices. St-Crustin and Pp-Crustin shared significant similarities with crustins of portunid crabs (68–95%) and other crabs (60–73%). Phylogenetic analysis showed that St-Crustin and Pp-Crustin possess the same ancestral origin and have a similar evolutionary status like other crustins, which has subsequently diverged at different phases of evolution. St-Crustin and Pp-Crustin were closely related to crab crustins rather than to the crustins of other crustacean groups. The wide distribution of crustins in crustaceans indicates the importance of these AMPs in the innate immunity. Discovery of novel crustins might pave way to the discovery of promising therapeutic/prophylactic agents in health management and disease control in crustacean aquaculture.