Mycobacterial MutT1-mediated dephosphorylation of the sensor histidine kinases reveals a new link in the regulation of the two-component signaling

Bacterial pathogens such as Mycobacterium tuberculosis majorly rely on two-component signaling (TCS) systems to sense and generate adaptive responses to the dynamic and stressful host environment. TCS comprises a sensor histidine kinase (SHK) that perceives the environmental signal and a response regulator (RR) that modulates the target gene expression. TCS occurs via a phosphotransfer event from SHK to RR. However, the mechanisms that regulate phosphotransfer events are not well understood. We explored the role of MutT1, originally characterized to hydrolyze oxidized GTP (8-oxo-GTP) and dGTP (8-oxo-dGTP), in TCS regulation. Unlike other MutT proteins, mycobacterial MutT1 comprises two domains (N-terminal domain, NTD; and C-terminal domain, CTD). Structurally, MutT1 NTD is like MutT proteins in other organisms. However, the MutT1 CTD is similar to Escherichia coli SixA, a histidine phosphatase with an Arg-His-Gly (RHG) motif. We show that MutT1 CTD dephosphorylates many SHKs and impacts expression of their target genes, highlighting the role of MutT1 in regulating TCS. These novel findings are of special significance because they provide us with an extrinsic phosphatase mechanism to reset TCS signaling. The study reveals an intricate interplay between an enzyme that sanitizes the cellular nucleotide pool and bacterial signaling pathways, offering insights into the adaptation mechanisms.