ABSTRACT
Objective To investigate the single nucleotide polymorphism (SNP) of toxinantitoxin-chaperone (TAC) system of Mycobacterium (M.) tuberculosis with different genotypes and its biological significance.Methods A total of 183 clinical M.tuberculosis isolates were collected for spoligotyping.The sequences of higA,higB and Rv1957 were obtained by using PCR and DNA sequencing.The sequences were compared for possible mutations.Functional consequences of nonsynonymous SNPs were predicted by using I-Mutant 2.0 servers.Results Among the 183 M.tuberculosis isolates,138(75.41％) belonged to the Beijing family,while 45(24.59％) belonged to the non-Beijing family.A total of 149(81.42％) isolates showed polymorphisms in the TAC system.We discovered 6 nonsynonymous SNPs and 2 synonymous SNPs.All the synonymous mutations occurred in higA gene,while nonsynonymous SNPs were found in the higA,higB and Rv1957 genes either.All the synonymous mutations and 4 nonsynonymous SNPs were restricted to the Beijing family strains and only 2 nonsynonymous SNPs were observed in the non-Beijing family strains.Of the 6 nonsynonymous SNPs studied,4 were predicted to have ability to affect the stability of respective protein.Conclusion The SNPs in the coding sequences of TAC system in clinical isolates can be relatively high and the Beijing family strains are with higher polymorphism,which might benefit to adapt to different host environment.