GrpE, a nucleotide exchange factor for DnaK.
The cochaperone GrpE functions as a nucleotide exchange factor to promote dissociation of adenosine 5'-diphosphate (ADP) from the nucleotide-binding cleft of DnaK. GrpE and the DnaJ cochaperone act in concert to control the flux of unfolded polypeptides into and out of the substrate-binding domain of DnaK by regulating the nucleotide-bound state of DnaK. DnaJ stimulates nucleotide hydrolysis, and GrpE promotes the exchange of ADP for adenosine triphosphate (ATP) and also augments peptide release from the DnaK substrate-binding domain in an ATP-independent manner. The eukaryotic cytosol does not contain GrpE per se because GrpE-like function is provided by the BAG1 protein, which acts as a nucleotide exchange factor for cytosolic Hsp70s. GrpE, which plays a prominent role in mitochondria, chloroplasts, and bacterial cytoplasms, is a fascinating molecule with an unusual quaternary structure. The long alpha-helices of GrpE have been hypothesized to act as a thermosensor and to be involved in the decrease in GrpE-dependent nucleotide exchange that is observed in vitro at temperatures relevant to heat shock. This review describes the molecular biology of GrpE and focuses on the structural and kinetic aspects of nucleotide exchange, peptide release, and the thermosensor hypothesis.
Harrison
Celia
C
Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA. harrison@bbri.org
D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins; D018832:Molecular Chaperones / Q000378:metabolism*; D017354:Point Mutation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013696:Temperature
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C068113:GrpE protein, Bacteria; C489400:GrpE protein, E coli; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C086039:MGE1 protein, S cerevisiae; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D018832:Molecular Chaperones; D029701:Saccharomyces cerevisiae Proteins; C063842:dnaK protein, E coli