An extracellular copper/zinc superoxide dismutase (ecCuZnSOD) from Chinese mitten crab, Eriocheir sinensis and its relationship with Spiroplasma eriocheiris

Abstract

An extracellular copper–zinc superoxide dismutase (ecCuZnSOD) gene was cloned from hemocytes of Chinese mitten crab, Eriocheir sinensis. The ecCuZnSOD cDNA consists of 891 bp with an open reading frame (ORF) of 624 bp that encodes 208 amino acids (aa) with 24 residues of a signal peptide sequence. The predicted molecular mass of the mature protein (184 aa) is 21.76 kDa with an estimated pI of 6.02. Amino acids are responsible for binding Cu (His90, 92, 109, and 171) and Zn (His109, 117, and 126, and Asp 129), two cysteines (95 and 189) that form a disulfide bond, two CuZnSOD signatures (GFHVHEWGVDGS) from 88 to 99 and (GNAGGRVACCTI) from 189 to 200. The deduced amino acid sequence of E. sinensis ecCuZnSOD showed similarity of 75% and 58.7% with the ecCuZnSOD of giant freshwater prawn Macrobrachium rosenbergii and mud crab Scylla serrata, respectively. Spiroplasma eriocheiris is a novel pathogen of tremor disease of E. sinensis. This paper also studied the relationship between E. sinensis ecCuZnSOD and S. eriocheiris. The ecCuZnSOD transcript in hemocytes significantly increased in 1 h, had returned to the original value by 24 h, and increased after 192 h by the S. eriocheiris inoculation. The ecCuZnSOD transcript increased significantly at 1 h after S. eriocheiris injection indicating induction of the immune system of the crab within a short time. After 192 h the ecCuZnSOD transcript increased, meanwhile the tremor symptom of the crab also appeared, induction of the ecCuZnSOD has relation with the immune response of hosts to resist S. eriocheiris.