title: Effect of hsp70 chaperone on the folding and misfolding of polypeptides modeling an elongating protein chain.
abstract: Virtually nothing is known about the interaction of co-translationally active chaperones with nascent polypeptides and the resulting effects on peptide conformation and folding. We have explored this issue by NMR analysis of apomyoglobin N-terminal fragments of increasing length, taken as models for different stages of protein biosynthesis, in the absence and presence of the substrate binding domain of Escherichia coli Hsp70, DnaK-beta. The incomplete polypeptides misfold and self-associate under refolding conditions. In the presence of DnaK-beta, however, formation of the original self-associated species is completely or partially prevented. Chaperone interaction with incomplete protein chains promotes a globally unfolded dynamic DnaK-beta-bound state, which becomes folding-competent only upon incorporation of the residues corresponding to the C-terminal H helix. The chaperone does not bind the full-length protein at equilibrium. However, its presence strongly disfavors the kinetic accessibility of misfolding side-routes available to the full-length chain. This work supports the role of DnaK as a "holder" for incomplete N-terminal polypeptides. However, as the chain approaches its full-length status, the tendency to intramolecularly bury non-polar surface efficiently outcompetes chaperone binding. Under these conditions, DnaK serves as a "folding enhancer" by supporting folding of a population of otherwise folding-incompetent full-length protein chains.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA.
authors.forename: Neşe
authors.initials: N
authors.lastname: Kurt
authors.forename: Senapathy
authors.initials: S
authors.lastname: Rajagopalan
authors.forename: Silvia
authors.initials: S
authors.lastname: Cavagnero
mesh_terms: D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D009211:Myoglobin / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D014176:Protein Biosynthesis; D017510:Protein Folding; D013816:Thermodynamics
chemical_list: D001059:Apoproteins; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D009211:Myoglobin; D010446:Peptide Fragments; D010455:Peptides; C010857:apomyoglobin; C063842:dnaK protein, E coli