First identification and characterization of a triple WAP domain containing protein in Procambarus clarkii provides new insights into the classification and evolution of WAP proteins in crustacean

Whey acidic protein domain (WAPD) is a usual motif in crustaceans, and is found mainly in the immune-related proteins. In the present study, a protein containing three tandem WAPDs was identified in red swamp crayfish Procambarus clarkii and designated as PcTWD. This is the first report of a protein of such domain architecture in crustaceans. Introducing the WAPDs of PcTWD into phylogenetic analysis led to the classification of crustacean WAP proteins into classical crustins and proteins containing solely WAPDs. PcTWD was widely expressed in multiple tissues, including hemocytes, gills, hepatopancreas, heart, stomach and intestine. Its expression could be significantly induced by Staphylococcus aureus or Aeromonas hydrophila challenge. Knockdown PcTWD expression by RNAi suppressed host resistance against A. hydrophila, while exogenous recombinant PcTWD could enhance the host immunity. The three WAPDs showed a labor division. The first two domains were responsible for the protease inhibitory activity, and the third domain contributed to the antimicrobial activity. Thus PcTWD was found as an important protein in crayfish antibacterial immunity.

Characterization of a type-I crustin with broad-spectrum antimicrobial activity from red swamp crayfish Procambarus clarkii

Crustins are a family of antimicrobial peptides mainly identified in crustaceans and characterized by a whey acidic protein (WAP) domain and an additional glycine-, cysteine-, or proline-rich region. In this study, we identified and characterized PcCru, a new crustin isolated from red swamp crayfish Procambarus clarkii. The open reading frame of PcCru was 333 base pairs long and encoded a 110-residue polypeptide, which contained a signal peptide, a cysteine-rich region, and a WAP domain. The architecture and phylogenetic analysis suggested that PcCru was a new member of the type-I crustin family. PcCru was highly expressed in hemocytes and was significantly induced by viral and bacterial stimulations at both the translational and transcriptional levels. The titer of PcCru in circulating plasma was also increased considerably by bacterial challenge. Recombinant PcCru from both prokaryotic and eukaryotic expression systems were generated, and the proteins exhibited broad-spectrum antimicrobial activity. Furthermore, PcCru protected crayfish from infection by pathogenic bacteria Aeromonas hydrophila in vivo. This study provided new information emphasizing the important role of the crustin family in the crustacean antibacterial immune response.

Differences in gene organization between type I and type II crustins in the morotoge shrimp, Pandalopsis japonica

Crustins are cysteine-rich cationic antimicrobial peptides (AMPs) found in decapod crustaceans. Six novel crustin genes (Paj-CrusIc, Id, Ie, If, IIb and IIc) were identified in the morotoge shrimp, Pandalopsis japonica. Deduced amino acid sequences of isolated Paj-Crus genes ranged from 99 to 178 amino acid residues (10.6-17.8 kDa). Sequence analysis of nine isolated Paj-Crus genes and 100 different crustins from various decapod crustaceans revealed that a splice site and KXXXCP motif within the WAP domain may be the main criteria for classifying type I and II crustins, suggesting that the two types of crustin genes may have been generated by different processes. We also identified three intron-less crustin I genes (Paj-Crus Id, Ie and If) for the first time, which may have been generated by gene duplication. The tissue distribution profiles showed that Paj-CrusI genes were expressed predominantly in the gill and epidermis, whereas Paj-CrusII genes were expressed ubiquitously, suggesting that the two types of crustins may play different roles in various tissues or under different physiological conditions. Differing from previous results, hemocyte-specific crustin was not isolated from Pandalopsis japonica. This study showed that both types of crustin genes (types I and II) exist in decapod crustaceans and their primary structure and expression profiles differ from each other, suggesting that they may play different biological roles. This will help to extend our knowledge of the crustacean innate immune response, which will provide important basic information of shrimp immunity against various pathogens.