A genetic analysis of the functional interactions within Mycobacterium tuberculosis single-stranded DNA binding protein.

ABSTRACT: Single-stranded DNA binding proteins (SSBs) are vital in all organisms. SSBs of Escherichia coli (EcoSSB) and Mycobacterium tuberculosis (MtuSSB) are homotetrameric. The N-terminal domains (NTD) of these SSBs (responsible for their tetramerization and DNA binding) are structurally well defined. However, their C-terminal domains (CTD) possess undefined structures. EcoSSB NTD consists of ?1-?1'-?2-?3-?-?4-?451-?452-?5 secondary structure elements. MtuSSB NTD includes an additional ?-strand (?6) forming a novel hook-like structure. Recently, we observed that MtuSSB complemented an E. coli ?ssb strain. However, a chimeric SSB (m?4-?5), wherein only the terminal part of NTD (?4-?5 region possessing L45 loop) of EcoSSB was substituted with that from MtuSSB, failed to function in E. coli in spite of its normal DNA binding and oligomerization properties. Here, we designed new chimeras by transplanting selected regions of MtuSSB into EcoSSB to understand the functional significance of the various secondary structure elements within SSB. All chimeric SSBs formed homotetramers and showed normal DNA binding. The m?4-?6 construct obtained by substitution of the region downstream of ?5 in m?4-?5 SSB with the corresponding region (?6) of MtuSSB complemented the E. coli strain indicating a functional interaction between the L45 loop and the ?6 strand of MtuSSB.

SUBMITTER: Rex K 

PROVIDER: S-EPMC3983218 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature