Distinct properties of Mycobacterium tuberculosis single-stranded DNA binding protein and its functional characterization in Escherichia coli

Single-stranded DNA binding proteins (SSBs) play an essential role in various DNA functions. Characterization of SSB from Mycobacterium tuberculosis, which infects nearly one-third of the world’s population and kills about 2–3 million people every year, showed that its oligomeric state and various in vitro DNA binding properties were similar to those of the SSB from Escherichia coli. In this study, use of the yeast two-hybrid assay suggests that the EcoSSB and the MtuSSB are even capable of heterooligomerization. However, the MtuSSB failed to complement a Δssb strain of E.coli. The sequence comparison suggested that MtuSSB contained a distinct C-terminal domain. The C-terminal domain of EcoSSB interacts with various cellular proteins. The chimeric constructs between the N- and C-terminal domains of the MtuSSB and EcoSSB exist as homotetramers and demonstrate DNA binding properties similar to the wild-type counterparts. Despite similar biochemical properties, the chimeric SSBs also failed to complement the Δssb strain of E.coli. These data allude to the occurrence of a ‘cross talk’ between the N- and the C-terminal domains of the SSBs for their in vivo function. Further, compared with those of the EcoSSB, the secondary/tertiary interactions within MtuSSB were found to be less susceptible to disruption by guanidinium hydrochloride. Such structural differences could be exploited for utilizing such essential proteins as crucial molecular targets for controlling the growth of the pathogen.