title: In vivo newly translated polypeptides are sequestered in a protected folding environment.
abstract: Molecular chaperones play a fundamental role in cellular protein folding. Using intact mammalian cells we examined the contribution of cytosolic chaperones to de novo folding. A large fraction of newly translated polypeptides associate transiently with Hsc70 and the chaperonin TRiC/CCT during their biogenesis. The substrate repertoire observed for Hsc70 and TRiC is not identical: Hsc70 interacts with a wide spectrum of polypeptides larger than 20 kDa, while TRiC associates with a diverse set of proteins between 30 and 60 kDa. Overexpression of a bacterial chaperonin 'trap' that irreversibly captures unfolded polypeptides did not interrupt the productive folding pathway. The trap was unable to bind newly translated polypeptides, indicating that folding in mammalian cells occurs without the release of non-native folding intermediates into the bulk cytosol. We conclude that de novo protein folding occurs in a protected environment created by a highly processive chaperone machinery and is directly coupled to translation.
authors.affiliation: Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA.
authors.forename: V
authors.initials: V
authors.lastname: Thulasiraman
authors.forename: C F
authors.initials: CF
authors.lastname: Yang
authors.forename: J
authors.initials: J
authors.lastname: Frydman
mesh_terms: D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D018834:Chaperonin 60 / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D017510:Protein Folding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D056427:t-Complex Genome Region
chemical_list: D002352:Carrier Proteins; D018834:Chaperonin 60; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D010455:Peptides; D011994:Recombinant Proteins; C116196:PPP1R11 protein, human; D044767:Ubiquitin-Protein Ligases