ClpB and HtpG facilitate de novo protein folding in stressed Escherichia coli cells.
DnaK-DnaJ-GrpE and GroEL-GroES are the best-characterized molecular chaperone systems in the cytoplasm of Escherichia coli. A number of additional proteins, including ClpA, ClpB, HtpG and IbpA/B, act as molecular chaperones in vitro, but their function in cellular protein folding remains unclear. Here, we examine how these chaperones influence the folding of newly synthesized recombinant proteins under heat-shock conditions. We show that the absence of either CIpB or HtpG at 42 degrees C leads to increased aggregation of preS2-beta-galactosidase, a fusion protein whose folding depends on DnaK-DnaJ-GrpE, but not GroEL-GroES. However, only the deltaclpB mutation is deleterious to the folding of homodimeric Rubisco and cMBP, two proteins requiring the GroEL-GroES chaperonins to reach a proper conformation. Null mutations in clpA or the ibpAB operon do not affect the folding of these model substrates. Overexpression of ClpB, HtpG, IbpA/B or ClpA does not suppress inclusion body formation by the aggregation-prone protein preS2-S'-beta-galactosidase in wild-type cells or alleviate recombinant protein misfolding in dnaJ259, grpE280 or groES30 mutants. By contrast, higher levels of DnaK-DnaJ, but not GroEL-GroES, restore efficient folding in deltaclpB cells. These results indicate that ClpB, and to a lesser extent HtpG, participate in de novo protein folding in mildly stressed E. coli cells, presumably by expanding the ability of the DnaK-DnaJ-GrpE team to interact with newly synthesized polypeptides.
Department of Chemical Engineering, University of Washington, Seattle 98195, USA.
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Baneyx
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018835:Chaperonin 10 / Q000378:metabolism; D018834:Chaperonin 60 / Q000378:metabolism; D049071:Endopeptidase Clp; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006514:Hepatitis B Surface Antigens / Q000096:biosynthesis / Q000235:genetics; D002479:Inclusion Bodies; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017510:Protein Folding; D011498:Protein Precursors / Q000096:biosynthesis / Q000235:genetics; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
D001426:Bacterial Proteins; D018835:Chaperonin 10; D018834:Chaperonin 60; C080369:CipA protein, Clostridium; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; C068113:GrpE protein, Bacteria; C489400:GrpE protein, E coli; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D006514:Hepatitis B Surface Antigens; C489352:HtpG protein, E coli; C097578:IbpA protein, E coli; C097579:IbpB protein, E coli; D008565:Membrane Proteins; D018832:Molecular Chaperones; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; C050807:presurface protein 2, hepatitis B surface antigen; C066720:HtpG protein, bacteria; D001616:beta-Galactosidase; D049071:Endopeptidase Clp; C063842:dnaK protein, E coli; C069775:ClpB protein, E coli