[Cloning and characterization of the gene encoding IMPDH of Streptococcus suis serotype 2]

Given the lack of effective vaccines to control Streptococcus suis infection and the lack of a rapid and reliable molecular diagnostic assay to detect its infection, S. suis serotype 2 was sequenced partly in an effort to identify important virulence factors. Two new open reading frames were found located between orf2 and mrp. One of new open reading frame (2738 - 3694) that encoded a polypeptide of 319 amino acid residues with a calculated molecular mass of 33.5kDa was identified by Western blot. GenBank database search revealed that the derived amino acid sequence shared low homology with sequences of known function from other genes. Second structure was analyzed by InterPro, PHD, DNAstar software, the deduced protein had functional domains typical of IMP dehydrogenase (IMPDH). The PCR product of the open reading frame was transformed into E. coli BL21 and the fusion protein of 48kDa was expressed. The recombinant protein was reactive with serum from pigs experimentally infected with virulent strains of S. suis type 2, suggesting that the protein is immunogenic. IMPDH activity staining confirmed that the protein has IMPDH function and can catalyze the rate-limiting reaction of GTP biosynthesis, the NAD-dependent reduction of IMP into XMP. Flow cytometry (FCM) revealed that the protein had apparent effect on HEp-2 cell cycle.