Region 2.1 of the Escherichia coli heat-shock sigma factor RpoH (sigma32) is necessary but not sufficient for degradation by the FtsH protease.
The cellular level of the Escherichia coli heat-shock sigma factor RpoH (sigma32) is negatively controlled by chaperone-mediated proteolysis through the essential metalloprotease FtsH. Point mutations in the highly conserved region 2.1 stabilize RpoH in vivo. To assess the importance of this turnover element, hybrid proteins were constructed between E. coli RpoH and Bradyrhizobium japonicum RpoH1, a stable RpoH protein that differs from region 2.1 of E. coli RpoH at several positions. Nine amino acids forming a putative alpha-helix were exchanged between the two proteins. Both hybrids were active sigma factors and showed intermediate protein stability. Introduction of RpoH region 2.1 into the general stress sigma factor RpoS, which is a substrate of the ClpXP protease, did not render RpoS susceptible to FtsH. Hence, region 2.1 alone is not sufficient to confer FtsH sensitivity to other proteins. Region 2.1 is not a major chaperone-binding site since DnaK and DnaJ bound efficiently to all RpoH variants. The in vivo stability of the mutated RpoH proteins correlated with their stability in a purified in vitro degradation system, suggesting that region 2.1 might be directly involved in the interaction with the FtsH protease.
Institute of Microbial Biology, Ruhr University Bochum, D-44780 Bochum, Germany.|Institute of Microbiology, ETH Zürich, Switzerland.
Markus
M
Obrist
Institute of Microbial Biology, Ruhr University Bochum, D-44780 Bochum, Germany.
Sonja
S
Milek
Institute of Microbiology, Free University Berlin, Germany.
Eberhard
E
Klauck
Institute of Microbiology, Free University Berlin, Germany.
Regine
R
Hengge
Institute of Microbial Biology, Ruhr University Bochum, D-44780 Bochum, Germany.|Institute of Microbiology, ETH Zürich, Switzerland.
Franz
F
Narberhaus
D049069:ATP-Dependent Proteases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D020369:Bradyrhizobium / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; C069774:heat-shock sigma factor 32; C069567:sigma factor KatF protein, Bacteria; D049069:ATP-Dependent Proteases; C513383:FtsH protein, E coli; C063842:dnaK protein, E coli