Genomic structure, expression pattern and functional characterization of crustinPm5, a unique isoform of crustin from Penaeus monodon

A unique isoform of crustin, crustinPm5, was identified from a gill-epipodite cDNA library of the tiger shrimp, Penaeus monodon. The crustinPm5 cDNA contains an open reading frame (ORF) of 510 bp encoding a 169 amino acid protein. The deduced amino acid sequence of crustinPm5 showed 38% and 37% overall sequence identity with those of crustinPm1 and crustin-likePm, respectively, two crustin isoforms previously reported. The crustinPm5 gene contained four exons interrupted by three introns whilst the upstream sequence contains a putative promoter with two potential binding sites for NF-κB, one complete heat-shock regulatory element (HSE) and five putative GATA factor binding sites. The transcripts of crustinPm5 were primarily observed in the epipodite and eyestalk and not in hemocytes. Expression analysis revealed that the transcript levels of crustinPm5, crustinPm1 and crustin-likePm in epipodite were up-regulated upon heat treatment and hyperosmotic salinity stress. The recombinant crustinPm5 exhibited antimicrobial activity against some Gram-positive bacteria in vitro, but did not inhibit the growth of any Gram-negative bacteria tested. These results, together with the transcript expression pattern, indicate a diverse function of the proteins in the crustin family particularly crustinPm5 that might function as a stress mediator in addition to its antibacterial action.