SecB-like chaperone controls a toxin–antitoxin stress-responsive system in Mycobacterium tuberculosis

Abstract

A major step in the biogenesis of newly synthesized precursor proteins in bacteria is their targeting to the Sec translocon at the inner membrane. In Gram-negative bacteria, the chaperone SecB binds nonnative forms of precursors and specifically transfers them to the SecA motor component of the translocase, thus facilitating their export. The major human pathogen Mycobacterium tuberculosis is an unusual Gram-positive bacterium with a well-defined outer membrane and outer membrane proteins. Assistance to precursor proteins by chaperones in this bacterium remains largely unexplored. Here we show that the product of the previously uncharacterized Rv1957 gene of M. tuberculosis can substitute for SecB functions in Escherichia coli and prevent preprotein aggregation in vitro. Interestingly, in M. tuberculosis, Rv1957 is clustered with a functional stress-responsive higB-higA toxin-antitoxin (TA) locus of unknown function. Further in vivo experiments in E. coli and in Mycobacterium marinum strains that do not possess the TA-chaperone locus show that the severe toxicity of the toxin was entirely inhibited when the antitoxin and the chaperone were jointly expressed. We found that Rv1957 acts directly on the antitoxin by preventing its aggregation and protecting it from degradation. Taken together, our results show that the SecB-like chaperone Rv1957 specifically controls a stress-responsive TA system relevant for M. tuberculosis adaptive response.DnaK | molecular chaperones | trigger factor | protease

YfgM Is an Ancillary Subunit of the SecYEG Translocon in Escherichia coli

“…Immediately after the addition of denatured proOmpC, aggregation was monitored continuously at 320 nm for 60 min at 25°C on a Cary Scan UV-visible spectrophotometer from Varian. All solutions used in this assay were filtered through a 0.22-m filter (35).…”

Protein Export by the Mycobacterial SecA2 System Is Determined by the Preprotein Mature Domain

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Chaperone addiction of toxin–antitoxin systems

“…To date, the TAC system of the major human pathogen Mycobacterium tuberculosis is the best characterized41012. It is encoded by three genes organized in an operon, Rv1955-Rv1956-Rv1957 , respectively, encoding the TA pair ( Mtb -HigB1 and Mtb- HigA1) and the Mtb -SecB TA chaperone1012.…”