Molecular cloning, characterization and expression analysis of S- adenosyl- L-homocysteine hydrolase (SAHH) during the pathogenic infection of Litopenaeus vannamei by Vibrio alginolyticus.

SAHH is an enzyme, playing a significant role in the catalyzation of the S-adenosyl homocysteine (SAH) into homocysteine (Hcy) and adenosine (Ado). However, little is known information of the enzyme in crustaceans. In the present study, SAHH cDNA was cloned from Litopenaeus vannamei (LvSAHH). The full length of the LvSAHH was found, containing a 5' UTR of 119 bp, an ORF of 1236 bp and a 3' UTR of 549 bp. The LvSAHH gene encoded a polypeptide of 411 amino acids with an estimated molecular mass of 45.55 kD and a predicted isoelectronic point (pI) of 5.63. Comparison of the deduced amino acid sequence showed that LvSAHH has high identity (70 %-82%) with other known species. qRT-PCR analysis revealed that LvSAHH mRNA was broadly expressed in all of the examined tissues, while the highest expression level was observed in muscle, followed by the expression in stomach, gill, pleopod, hepatopancreas, heart, eye and intestine. Subcellular localization analysis revealed that LvSAHH was predominantly localized in the cytoplasm and nucleus. LvSAHH mRNA expression levels in hepatopancreas and gill were significantly up-regulated from 6 to 48 h after V. alginolyticus injection and reached the highest level (15-fold and 8-fold, p < 0.01) at 24 h, respectively. Additionally, the Toll-like receptors (TLR) and interleukins-16 (IL-16) were detected in hepatopancreas and gill of LvSAHH-knockdown SAHH. LvRack1, LvToll1, LvToll2, LvToll3 and LvIL-16 transcripts were decreased significantly in LvSAHH-knockdown shrimp at 24 h post V. alginolyticus stimulation in hepatopancreas and gill. But LvToll3 was no significant difference in gill. In summary, these results indicated that LvSAHH may play a regulatory role in the invertebrate innate immune defense by regulating TLR and IL-16 expression.