Molecular Cloning and Functional Analysis of Secretory Phospholipase A from Apostichopus japonicus.

Secretory phospholipase A (sPLA) plays important roles in phospholipid metabolism, skin barrier maintenance, immune response and other processes in organisms. sPLA of sea cucumber A. japonicus (AjPLA) has not yet been reported. This study successfully amplified the AjPLA sequence. The total cDNA of AjPLA is 931 bp, including a 480 bp ORF that encodes 159 amino acids. The AjPLA protein includes a 16-aa signal peptide, a 5-aa precursor peptide and a 138-aa mature peptide. Homologous alignment showed that AjPLA and the sPLAs from starfish have the typical domains of the Group IB sPLA. And additional amino acid sequences were found around the β-Wing, which is different from the Group IB sPLA. These results showed that AjPLA and sPLAs from starfish all belong to a new group in the Group I sPLA family. AjPLA is widely distributed in sea cucumber tissues. The functional analysis also showed that AjPLA 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 were significantly increased in V. splendens-infected sea cucumbers. The results indicated that AjPLA 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 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 gene function in vivo, development and application of AjPLA protein.