Identification and characterization of spiralin-like protein SLP25 from Spiroplasma eriocheiris

Spiroplasma eriocheiris causes tremor disease (TD) of Chinese mitten crab Eriocheir sinensis, but little is known about the molecular characterization of this pathogen. The present study was undertaken to identify a unique gene of spiroplasma, spiralin-like protein (SLP25) and analyze its character. The full-length DNA of SLP25 is 699 bp encodes a protein of 232 amino acid residues. The theoretical isoelectric point and molecular weight for the SLP25 are 4.50 and 24.67 kDa, respectively. The similarity of SLP25 deduced amino acid sequence, shared with the spiralin from other species, indicated that the gene might be a member of the spiralin family. After cloning the SLP25, the gene was site-mutated from TGA to TGG and transcribed in E. coli to full expression of the recombinant SLP25. Anti-SLP25 serum was prepared by immunization of rabbits. The titer of anti-SLP25 serum was about 1:20000. A SLP25 band was detected by anti-SLP25 antibody using the total proteins of S. eriocheiris. A specific immunoreactive band was detected when anti-S. eriocheiris serum was opposed to the recombinant protein. This finding suggests that SLP25 could be a good antigen for immunodiagnosis of TD of E. sinensis.