Molecular Cloning and Functional Analysis of Secretory Phospholipase A2 from Apostichopus japonicus

Secretory phospholipase A(2) (sPLA(2)) plays important roles in phospholipid metabolism, skin barrier maintenance, immune response and other processes in organisms. sPLA(2) of sea cucumber A. japonicus (AjPLA(2)) has not yet been reported. This study successfully amplified the AjPLA(2) sequence. The total cDNA of AjPLA(2) is 931 bp, including a 480 bp ORF that encodes 159 amino acids. The AjPLA(2) protein includes a 16-aa signal peptide, a 5-aa precursor peptide and a 138-aa mature peptide. Homologous alignment showed that AjPLA(2) and the sPLA(2)s from starfish have the typical domains of the Group IB sPLA(2). And additional amino acid sequences were found around the beta-Wing, which is different from the Group IB sPLA(2). These results showed that AjPLA(2) and sPLA(2)s from starfish all belong to a new group in the Group I sPLA(2) family. AjPLA(2) is widely distributed in sea cucumber tissues. The functional analysis also showed that AjPLA2 was upregulated in the intestine by feeding. When the body wall was damaged, it was significantly upregulated around the wound. And the expression levels of AjPLA(2) were significantly increased in V. splendens-infected sea cucumbers. The results indicated that AjPLA(2) plays roles in the sea cucumber immunologic process. Combined with the upregulation of unsaturated fatty acids (PUFAs) content in A. japonicus, it demonstrated that AjPLA(2) could participate in the immune of A. japonicus by hydrolyzing phospholipid and releasing PUFAs. This study had a solid foundation for the further research of AjPLA(2) gene function in vivo, development and application of AjPLA(2) protein.