Mycobacterium tuberculosis Rv1474c is a TetR-like transcriptional repressor that regulates aconitase, an essential enzyme and RNA-binding protein, in an iron-responsive manner

Abstract

Mycobacterium tuberculosis (M.tb), tuberculosis (TB) causing bacteria, employs several mechanisms to maintain iron homeostasis which is critical for its survival and pathogenesis. M.tb aconitase (Acn), a [4Fe-4S] cluster-containing essential protein, apart from participating in energy cycle, also binds to predicted iron-responsive RNA elements. In this study, we identified Rv1474c as a regulator of its operonic partner acn and carried out its biochemical and functional characterization. The binding motif for Rv1474c in the upstream region of acn (Rv1475c)-Rv1474c operon was verified by gel-shift assays. Reporter assays in E. coli followed by over-expression studies in mycobacteria, using both wild type and a DNA-binding defective mutant, demonstrated Rv1474c as a Tet-R like repressor of acn. Rv1474c, besides binding tetracycline, could also bind iron which negatively influenced its DNA binding activity. Further, a consistent decrease in the relative transcript levels of acn when M.tb was grown in iron-deficient conditions as compared to either normal or other stress conditions, indicated regulation of acn by Rv1474c in an iron-responsive manner in vivo. The absence of homologs in the human host and its association with indispensable iron homeostasis makes Rv1474c an attractive target for designing novel anti-mycobacterials.

Keywords: Iron homeostasis; Iron-responsive-proteins; M.tb aconitase; TetR; Transcription factors.