Expression of glutamine synthetase in Tegillarca granosa (Bivalvia, Arcidae) hemocytes stimulated by Vibrio parahaemolyticus and lipopolysaccharides.

The blood cockle, Tegillarca granosa, is a widely consumed clam in the Indo-Pacific region. Glutamine synthetase ( GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine. We identified the GS of T. granosa ( Tg-GS) from hemocytes by 3'-and 5'-rapid amplification of cDNA ends ( RACE)-PCR. The fulllength cDNA consisted of 1762 bp, with a 1104-bp open reading frame encoding 367 amino acids. Sequence comparison showed that Tg-GS has homology to GS of other organisms, with 79.78% identity with GS from the Pacific oyster Crassostrea gigas, 71.98% identity with GS from the zebrafish Danio rerio, and 68.96% identity with human Homo sapiens GS. A C-beta-Grasp domain and an N-catalytic domain were identified in Tg-GS, indicating that Tg-GS should be classified as a new member of the GS family. A quantitative RT-PCR assay was used to detect mRNA expression of Tg-GS in five different tissues. Higher levels of mRNA expression of GS were detected in the tissues of hemocytes and the mantle. Up- regulation of GS by challenge with the bacteria Vibrio parahaemolyticus and with bacterial wall lipopolysaccharides showed that GS plays a role in anti-bacterial immunity. We conclude that pathogen infection significantly induces expression level of Tg-GS, and that activation of GS influences the immune response of T. granosa by increasing glutamine concentration.