title: Quasi-native chaperonin-bound intermediates in facilitated protein folding.
abstract: Chaperonins are known to facilitate protein folding, but their mechanism of action is not well understood. The fact that target proteins are released from and rebind to different chaperonin molecules ("cycling") during a folding reaction suggests that chaperonins function by unfolding aberrantly folded molecules, allowing them multiple opportunities to reach the native state in bulk solution. Here we show that the cycling of alpha-tubulin by cytosolic chaperonin (c-cpn) can be uncoupled from the action of cofactors required to complete the folding reaction. This results in the accumulation of folding intermediates which are chaperonin-bound, stable, and quasi-native in that they bind GTP nonexchangeably. We present evidence that these intermediates can be generated without the target protein leaving c-cpn. These data show that, in contrast to prevailing models, target proteins can maintain, and possibly acquire, significant native-like structure while chaperonin-bound.
authors.affiliation: Department of Biochemistry, New York University Medical Center, New York 10016, USA.
authors.forename: G
authors.initials: G
authors.lastname: Tian
authors.forename: I E
authors.initials: IE
authors.lastname: Vainberg
authors.forename: W D
authors.initials: WD
authors.lastname: Tap
authors.forename: S A
authors.initials: SA
authors.lastname: Lewis
authors.forename: N J
authors.initials: NJ
authors.lastname: Cowan
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient; D018833:Chaperonins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008715:Methionine / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D014176:Protein Biosynthesis; D017510:Protein Folding; D012333:RNA, Messenger / Q000378:metabolism; D013462:Sulfur Radioisotopes; D014158:Transcription, Genetic; D014404:Tubulin / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D010761:Phosphorus Radioisotopes; D012333:RNA, Messenger; D013462:Sulfur Radioisotopes; D014404:Tubulin; D006160:Guanosine Triphosphate; D008715:Methionine; D018833:Chaperonins