title: Solution small-angle X-ray scattering study of the molecular chaperone Hsc70 and its subfragments.
abstract: Solution X-ray scattering experiments have been carried out on recombinant bovine Hsc70 (with 650 amino acid residues), a 60 kDa subfragment (residues 1-554) which has ATPase- and peptide-binding activities, a 44kDa subfragment (residues 1-386) which has only ATPase activity, and a peptide-binding fragment (residues 388-554). Modeling based on steady-state values of radii of gyration (Rg's) and P(r) functions shows that the 44 kDa and peptide-binding domains are oblate fragments while Hsc70 and the 60 kDa fragment are prolate and relatively elongated. Rg values decrease significantly in the presence of MgATP relative to their values in the presence of MgADP (delta Rg approximately 4-5 A) for Hsc70 and the 60 kDa fragment; in contrast, they are essentially equal in the presence of either nucleotide for the 44 kDa ATPase fragment. The kinetics of the change of Rg for Hsc70 and the 60 kDa fragment under single-ATPase cycle conditions show that the transition to the ATP-induced Rg occurs significantly more rapidly than ATP hydrolysis while the reverse transition to the larger Rg value does not occur before product release. Altogether, the solution scattering data support a model in which a conformational change in Hsc70 (presumably to the low-peptide-affinity state) is predicated on ATP binding while the reverse transition is predicated on product release.
authors.affiliation: Beckman Laboratories for Structural Biology, Department of Structural Biology, Stanford University School of Medicine, California 94305-5400, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Wilbanks
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.forename: H
authors.initials: H
authors.lastname: Tsuruta
authors.forename: K O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: D B
authors.initials: DB
authors.lastname: McKay
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002417:Cattle; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D009068:Movement; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D014965:X-Rays
chemical_list: D002352:Carrier Proteins; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D010446:Peptide Fragments; D010455:Peptides; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases