Crustin

Crustin is the common name for a family of antimicrobial peptides produced by crustaceans such as shrimp, crabs, and lobsters. These small, secreted proteins are part of the innate immune system and help defend against bacterial and fungal infections. Crustin genes are expressed in tissues including hemocytes, gill, and gut, and are upregulated in response to microbial challenge. Mature crustins typically contain an N-terminal signal peptide, followed by a variable region rich in glycine, and a conserved cysteine-rich domain at the C-terminus. A large subset of crustins also carries a whey acidic protein (WAP) four-disulfide core domain, a motif associated with antiprotease activity in many species. Structural diversity exists among crustins; some members have a WAP domain, while others lack it, reflecting functional diversification.

Antimicrobial activity of crustins has been demonstrated against a range of Gram-positive bacteria, and in several cases against Gram-negative bacteria and fungi. Mechanisms appear to include binding to bacterial cell surfaces, disruption of membranes, and/or interference with cell wall processes, as well as binding to lipopolysaccharide or lipoteichoic acid to neutralize endotoxins. The precise mechanism and spectrum can vary by species and crustin type.

In aquaculture and research, crustins are studied for their roles in disease resistance and as potential templates for novel antimicrobial agents. They are also used as markers of immune status in crustaceans. Further work aims to clarify the diversity, regulation, and functional specialization of crustin family members across species.