Convergence of two global regulators to coordinate expression of essential virulence determinants of Mycobacterium tuberculosis

Cyclic AMP (cAMP) is known to function as a global regulator of M. tuberculosis gene expression. Sequence-based transcriptomic profiling identified the mycobacterial regulon controlled by the cAMP receptor protein, CRP. In this study, we identified a new subset of CRP-associated genes including virulence determinants which are also under the control of a major regulator, PhoP. Our results suggest that PhoP as a DNA binding transcription factor, impacts expression of these genes, and phosphorylated PhoP promotes CRP recruitment at the target promoters. Further, we uncover a distinct regulatory mechanism involving CRP and PhoP on transcriptional control of these genes. While both these regulators influence gene expression, we show that activation of these genes requires direct recruitment of both PhoP and CRP at their target promoters. The most fundamental biological insight is derived from the inhibition of CRP binding at the regulatory regions in a PhoP-deleted strain owing to CRP-PhoP protein-protein interactions. Based on these results, a model is proposed suggesting how CRP and PhoP function as co-activators and contribute to activation of the essential pathogenic determinants. Together, these results uncover a novel mechanism where two interacting virulence factors impact expression of virulence determinants, have significant implications on TB pathogenesis.