Role of the response regulator RssB in sigma recognition and initiation of sigma proteolysis in Escherichia coli.
In growing Escherichia coli cells, the master regulator of the general stress response, sigmaS (RpoS), is subject to rapid proteolysis. In response to stresses such as sudden carbon starvation, osmotic upshift or shift to acidic pH, sigmaS degradation is inhibited, sigmaS accumulates and numerous sigmaS-dependent genes with stress-protective functions are activated. sigmaS proteolysis is dependent on ClpXP protease and the response regulator RssB, whose phosphorylated form binds directly to sigmaS in vitro. Here, we show that substitutions of aspartate 58 (D58) in RssB, which result in higher sigmaS levels in vivo, produce RssB variants unable to bind sigmaS in vitro. Thus, RssB is the direct substrate recognition factor in sigmaS proteolysis, whose affinity for sigmaS depends on phosphorylation of its D58 residue. RssB does not dimerize or oligomerize upon this phosphorylation and sigmaS binding, and RssB and sigmaS exhibit a 1:1 stoichiometry in the complex. The receiver as well as the output domain of RssB are required for sigmaS binding (as shown in vivo and in vitro) and for complementation of an rssB null mutation. Thus, the N-terminal receiver domain plays an active and positive role in RssB function. Finally, we demonstrate that RssB is not co-degraded with sigmaS, i.e. RssB has a catalytic role in the initiation of sigmaS turnover. A model is presented that integrates the details of RssB-sigmaS interaction, the RssB catalytic cycle and potential stress signal input in the control of sigmaS proteolysis.
Klauck
E
E
Department of Biology, Microbiology, Freie Universität Berlin, Königin-Luise-Str. 12-16, 14195 Berlin, Germany.
Lingnau
M
M
Hengge-Aronis
R
R
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins; D049071:Endopeptidase Clp; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D009154:Mutation; D033902:Periplasmic Binding Proteins; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors
D001426:Bacterial Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D033902:Periplasmic Binding Proteins; D011994:Recombinant Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C098923:rssB protein, E coli; C069567:sigma factor KatF protein, Bacteria; C074783:osmY protein, E coli; D012697:Serine Endopeptidases; C483573:ClpXP protease, E coli; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases