Toxin-antitoxin system promoter binding by type IV antitoxins of Mycobacterium tuberculosis

Tuberculosis remains a global health concern that requires difficult and lengthy treatment regimens for latent and persistent infection. Toxin-antitoxin systems have been linked to controlling bacterial growth rate and also implicated in bacterial persistence. Mycobacterium tuberculosis carries three uncharacterised type IV toxin-antitoxin systems, rv0837c/rv0836c, rv1044/rv1045, and rv2827c/rv2826c, which are regulated during macrophage infection. This work characterises the DNA-binding capabilities of Mycobacterium tuberculosis protein antitoxins Rv0837c, Rv1044, Rv2827c, and a homologue AbiEi from Streptococcus agalactiae, with the aim of developing the autoregulatory paradigm for type IV antitoxins. Biochemical analysis of AbiEi corroborated already published work and structural characterisation of AbiEi was begun. Rv2827c demonstrated an ability to bind four sites within the rv2827c cognate promoter with differing affinities, and is the first example of a negatively cooperative autoregulatory response within toxin-antitoxin systems. Rv0837c could not be expressed in E. coli and Rv1044 could only bind to the abiEi promoter indicating a structural relationship to AbiEi. The functional relevance of these data are unclear, but given the essentiality of Rv2827c these results prompt further study into this family of systems.