title: A model of protein targeting mediated by immunophilins and other proteins that bind to hsp90 via tetratricopeptide repeat domains.
abstract: We have shown recently that the immunophilins CyP-40 and FKBP52/hsp56 bind to a common site on hsp90 and that they exist in separate heterocomplexes with the glucocorticoid receptor (GR). FKBP52/hsp56 binds to hsp90 via its tetratricopeptide repeat (TPR) domains, it is not required for GR.hsp90 heterocomplex assembly, and it is thought to play a role in targeted movement of the GR. In this work we examine the hsp90 binding of four proteins (FKBP52/hsp56, CyP-40, p50, Mas70p) thought to be involved in targeted protein trafficking. FKBP52/hsp56 and CyP-40 (each with three TPRs), localize to the nucleus and nucleoli, respectively, and form relatively weak complexes with hsp90 that are competed by a CyP-40 fragment containing its three TPRs. The p50 component of the Src.hsp90 and Raf.hsp90 heterocomplexes localizes to cytoskeletal fibers extending from the perinuclear region to the plasma membrane and forming a rim under the plasma membrane of endothelial cells. p50, Mas70p (seven TPRs), which is a receptor for mitochondrial import, and the p60 (six to eight TPRs) component of the steroid receptor.hsp90 heterocomplex assembly system bind very tightly to hsp90 in a manner that is not competed by the CyP-40 fragment. However, bacterially expressed p60 blocks the binding of p50, Mas70p, FKBP52/hsp56, and CyP-40 to purified hsp90. The data are consistent with binding of all of these proteins to a site on hsp90 that is a general TPR domain acceptor. Our localization and binding data are used to develop a model in which proteins that are chaperoned by hsp90 move as dynamic complexes to their cellular sites of action, with the TPR-containing protein participating in targeting the movement of the complexes.
authors.affiliation: Department of Pharmacology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, USA.
authors.forename: J K
authors.initials: JK
authors.lastname: Owens-Grillo
authors.forename: M J
authors.initials: MJ
authors.lastname: Czar
authors.forename: K A
authors.initials: KA
authors.lastname: Hutchison
authors.forename: K
authors.initials: K
authors.lastname: Hoffmann
authors.forename: G H
authors.initials: GH
authors.lastname: Perdew
authors.forename: W B
authors.initials: WB
authors.lastname: Pratt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008954:Models, Biological; D008969:Molecular Sequence Data; D011485:Protein Binding; D011817:Rabbits; D051381:Rats; D012091:Repetitive Sequences, Nucleic Acid; D016559:Tacrolimus / Q000378:metabolism; D022021:Tacrolimus Binding Proteins
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D022021:Tacrolimus Binding Proteins; D016559:Tacrolimus