title: Setting the chaperonin timer: a two-stroke, two-speed, protein machine.
abstract: In a study of the timing mechanism of the chaperonin nanomachine we show that the hemicycle time (HCT) is determined by the mean residence time (MRT) of GroES on the cis ring of GroEL. In turn, this is governed by allosteric interactions within the trans ring of GroEL. Ligands that enhance the R (relaxed) state (residual ADP, the product of the previous hemicycle, and K(+)) extend the MRT and the HCT, whereas ligands that enhance the T (taut) state (unfolded substrate protein, SP) decrease the MRT and the HCT. In the absence of SP, the chaperonin machine idles in the resting state, but in the presence of SP it operates close to the speed limit, set by the rate of ATP hydrolysis by the cis ring. Thus, the conformational states of the trans ring largely control the speed of the complete chaperonin cycle.
authors.affiliation: Department of Chemistry and Biochemistry, Center for Biological Structure and Organization, University of Maryland, College Park, MD 20742, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Grason
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Gresham
authors.forename: George H
authors.initials: GH
authors.lastname: Lorimer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000494:Allosteric Regulation; D018835:Chaperonin 10 / Q000378:metabolism*; D018834:Chaperonin 60 / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D006868:Hydrolysis; D007700:Kinetics; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D013997:Time Factors
chemical_list: D018835:Chaperonin 10; D018834:Chaperonin 60; D000255:Adenosine Triphosphate; D011188:Potassium