Crustins

Crustins are a family of antimicrobial peptides produced by crustaceans, including shrimp, crabs, lobsters, and crayfish. They form part of the innate immune system and contribute to defense against bacterial and fungal pathogens. Crustins are typically secreted into the hemolymph and mucosal surfaces following immune challenge and can act rapidly to limit infection.

Most crustins are small, cationic peptides of roughly 100 amino acids after processing. They commonly contain a signal peptide for secretion, a glycine-rich region, and a cysteine-rich domain that includes a whey acidic protein (WAP) motif. Crustins are often categorized into several types based on their domain architecture, with some variants lacking a glycine-rich region and others defined by the presence of an isolated WAP domain. This structural diversity is thought to influence their antimicrobial spectrum and regulatory patterns.

Mechanistically, crustins exert activity through their cationic, amphipathic nature, which facilitates interaction with microbial membranes, potentially causing disruption or pore formation. They may also bind lipopolysaccharides and modulate immune responses. Antimicrobial activity can vary, with many crustins showing stronger effects against Gram-positive bacteria, while others display broader spectra that include Gram-negative bacteria and fungi. Expression is often tissue- and time-dependent and can be upregulated in hemocytes, gills, or hepatopancreas after infection or stress.

Crustins are distributed across many crustacean taxa and have been studied in species such as Penaeus monodon, Litopenaeus vannamei, Carcinus maenas, and other decapods. They are of interest for aquaculture as potential alternatives to conventional antibiotics and as biomarkers of immune status, with ongoing research into engineering and therapeutic applications.