The arginine kinase in Zhikong scallop Chlamys farreri is involved in immunomodulation

Arginine kinase (AK) catalyzes the reversible phosphorylation of l-arginine to form phosphoarginine, and plays a critical role in energy metabolism in invertebrates. In the present study, a scallop AK gene was identified from Chlamys farreri with an open reading frame (ORF) of 1101 bp encoding for a protein of 366 amino acids (designed as CfAK). An ATP-gua PtransN domain which was described as a guanidine substrate specificity domain (GS domain) and an ATP-gua Ptrans domian which was responsible for binding ATP, were both identified in CfAK. The mRNA transcripts of CfAK were detectable in haemocytes, hepatopancreas, adductor muscle, mantle, gill, kidney and gonad, with the highest expression level in the muscle and the lowest level in the hemocytes. The expression level of CfAK mRNA increased from fertilized eggs to eyebot, and reached the highest in the trochophore stage. The relative expression level of CfAK mRNA in muscle was up-regulated significantly after LPS (0.5 mg/mL) stimulation, and reached the peak at 6 h (5.2-fold, P < 0.05). The activity of inducible nitric oxide synthase (iNOS) in the supernatant of muscle homogenate increased significantly from 3.2 U/mg at 0 h to 9.7 U/mg at 12 h after LPS stimulation, while the concentration of nitric oxide (NO) in the supernatant of muscle homogenate began to increase at 3 h (21.55 μmol/L), and reached the top concentration at 24 h (42.27 μmol/L), then recovered to the normal level after 48 h. The recombinant protein of CfAK (rCfAK) expressed in Escherichia coli displayed Arginine kinase activity, and its apparent Km was 0.82 ± 0.11 and 1.24 ± 0.13 mM for l-arginine and ATP-Na, respectively. The results indicated that the CfAK was involved in energy production and utilization during the whole life process, and might refer to the immunomodulation process via altering the NO concentration and iNOS activity in scallop Chlamys farreri.

► A scallop AK gene was identified from Chlamys farreri.
► CfAK was ubiquitously expressed in larvae stage and various tissues of adults.
► The expression of CfAK could be induced by immune stimulation.
► CfAK was involved in energy production and utilization during the whole life process.
► CfAK regulated the NO concentration and iNOS activity, and involved in immunomodulation.