Comparative sequence analysis of crustin isoform MjCRS7 and MjWFDC-like gene from kuruma shrimp Marsupenaeus japonicus shows variant of the WFDC domain

Marine Arthropods as a Source of Antimicrobial Peptides

Peptide therapeutics play a key role in the development of new medical treatments. The traditional focus on endogenous peptides has shifted from first discovering other natural sources of these molecules, to later synthesizing those with unique bioactivities. This review provides concise information concerning antimicrobial peptides derived from marine crustaceans for the development of new therapeutics. Marine arthropods do not have an adaptive immune system, and therefore, they depend on the innate immune system to eliminate pathogens. In this context, antimicrobial peptides (AMPs) with unique characteristics are a pivotal part of the defense systems of these organisms. This review covers topics such as the diversity and distribution of peptides in marine arthropods (crustacea and chelicerata), with a focus on penaeid shrimps. The following aspects are covered: the defense system; classes of AMPs; molecular characteristics of AMPs; AMP synthesis; the role of penaeidins, anti-lipopolysaccharide factors, crustins, and stylicins against microorganisms; and the use of AMPs as therapeutic drugs. This review seeks to provide a useful compilation of the most recent information regarding AMPs from marine crustaceans, and describes the future potential applications of these molecules.

A novel type I Crustin from Exopalaemon carinicauda: Antimicrobial ability related to conserved cysteine

Crustins are a kind of antibacterial peptides (AMP) existing in crustaceans, and their antibacterial abilities are considered to be related to the conserved WAP domain. In this study, a novel type I Crustin gene was identified in Exopalaemon carinicauda, named EcCru. The deduced amino acid sequence revealed that the conserved cysteine at position 7 in the WAP domain was replaced by aspartic acid. The gene is 405 bp in length, encoding 134 amino acids, and is mainly distributed in gills and hepatopancreas. After Vibrio parahaemolyticus and Aeromonas hydrophila stimulation, the expression of EcCru was significantly up-regulated within 12 h, and then returned to normal levels. The recombinant protein was obtained using the Pichia pastoris expression system, and the recombinant protein had neither antibacterial activity against gram-positive or gram-negative bacteria. But the antibacterial ability emerged when Asp¹⁰¹ was mutated to Cys. Notably, we also obtained a mutant that had a deletion at the 6 th conserved Cys in the WAP domain, and this mutant had antibacterial ability against gram-positive bacteria Bacillus subtilis and B. cereus. This indicates that the conserved cysteine with different positions in WAP domain can have different effects on the antibacterial ability of Crustins.

Identification of two carcinin isoforms (MnCarc1 and MnCarc2) and their function in the antimicrobial immunity of Macrobrachium nipponense

Carcinin, a member of the crustin family, plays important roles in crustacean innate immunity. In this study, we identified two carcinin isoforms (MnCarc1 and MnCarc2) produced by alternative splicing from Macrobrachium nipponense. The full length of MnCarc1 and MnCarc2 cDNA are 1554 and 1495 bp with 687 and 609 bp open reading frame-encoding proteins that contain 228 and 202 amino acids, respectively. The genome of carcinin has nine exons and eight introns. MnCarc1 transcript contains all nine exons, whereas MnCarc2 only contains eight exons and lacks exon 4. MnCarc1 and MnCarc2 proteins contain a signal peptide, cysteine-rich regions, and a whey acidic protein domain. The phylogenetic tree shows that MnCarc1 and MnCarc2 are not grouped with other crustins and carcinins. MnCarc1 and MnCarc2 form a subgroup. MnCarc1 and MnCarc2 are widely distributed in various tissues. The expression of MnCarc1 and MnCarc2 were evidently upregulated at multiple time points in hemocytes and the intestine of M. nipponense after white spot syndrome virus, Vibrio parahaemolyticus, and Staphylococcus aureus challenges. Further studies showed that knockdown of MnDorsal or MnStat transcription factor could remarkably inhibit the upregulated expression of MnCarc1 and MnCarc2 caused by viral or bacterial challenges. In addition, recombinant MnCarc1 and MnCarc2 proteins could bind to various bacteria and polysaccharides and inhibit the growth of S. aureus and V. parahaemolyticus in vitro. This study indicated that carcinins from M. nipponense were involved in prawns innate immunity.

A new antimicrobial peptide isoform, Pc-crustin 4 involved in antibacterial innate immune response in fresh water crayfish, Procambarus clarkii

The main advantage of antimicrobial peptides (AMPs) used as the effectors in the innate immunity system of invertebrates is that the high specificity is not indispensable. And they play important roles in the systemic defenses against microbial invasion. In this study, a new full-length cDNA of the crustins molecule was identified in red swamp crayfish, P. clarkii (named Pc-crustin 4). The ORF of Pc-crustin 4 contained 369 bp which encoded a protein of 122 amino acids, with a 20-amino-acid signal peptide sequence. On the base of the classification method established by Smith et al., Pc-crustin 4 belonged to Type Ⅰ crustin molecule. The Pc-crustin 4 transcripts were expressed in hemocytes at relatively high level, and relatively low level in hepatopancreas, gills, and intestine in normal crayfish. After respectively challenged with S. aureus or E. ictaluri, the expression levels of Pc-crustin 4 showed up-regulation trends at different degrees in the hemocytes, hepatopancreas, gills, and intestine tissues. Besides, the results of liquid antibacterial assay showed that rPc-crustin 4 inhibited obviously the growth of S. aureus and E. ictaluri. The results of bacteria binding assay showed that rPc-crustin 4 could bind strongly to S. aureus and E. ictaluri. Finally, RNAi assay was performed to study the immunity roles of Pc-crustin 4 in crayfish in vivo. Taken together, Pc-crustin 4 is an important immunity effector molecule, which plays crucial roles in defending against bacterial infection in crayfish.