title: Substrate protein switches GroE chaperonins from asymmetric to symmetric cycling by catalyzing nucleotide exchange.
abstract: The complex kinetics of Pi and ADP release by the chaperonin GroEL/GroES is influenced by the presence of unfolded substrate protein (SP). Without SP, the kinetics of Pi release are described by four phases: a "lag," a "burst" of ATP hydrolysis by the nascent cis ring, a "delay" caused by ADP release from the nascent trans ring, and steady-state ATP hydrolysis. The release of Pi precedes the release of ADP. The rate-determining step of the asymmetric cycle is the release of ADP from the trans ring of the GroEL-GroES1 "bullet" complex that is, consequently, the predominant species. In the asymmetric cycle, the two rings of GroEL function alternately, 180° out of phase. In the presence of SP, a change in the kinetic mechanism occurs. With SP present, the kinetics of ADP release are also described by four phases: a lag, a "surge" of ADP release attributable to SP-induced ADP/ATP exchange, and a "pause" during which symmetrical "football" particles are formed, followed by steady-state ATP hydrolysis. SP catalyzes ADP/ATP exchange on the trans ring. Now ADP release precedes the release of Pi, and the rate-determining step of the symmetric cycle becomes the hydrolysis of ATP by the symmetric GroEL-GroES2 football complex that is, consequently, the predominant species. A FRET-based analysis confirms that asymmetric GroEL-GroES1 bullets predominate in the absence of SP, whereas symmetric GroEL-GroES2 footballs predominate in the presence of SP. This evidence suggests that symmetrical football particles are the folding functional form of the chaperonin machine in vivo.
authors.affiliation: Center for Biological Structure and Organization and Department of Chemistry and Biochemistry.
authors.forename: Xiang
authors.initials: X
authors.lastname: Ye
authors.forename: George H
authors.initials: GH
authors.lastname: Lorimer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D018835:Chaperonin 10 / Q000235:genetics / Q000378:metabolism*; D018834:Chaperonin 60 / Q000235:genetics / Q000378:metabolism*; D003374:Coumarins; D031541:Fluorescence Resonance Energy Transfer; D006868:Hydrolysis; D007700:Kinetics; D007768:Lactalbumin; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense / Q000235:genetics; D028044:Phosphate-Binding Proteins / Q000378:metabolism; D017510:Protein Folding
chemical_list: D018835:Chaperonin 10; D018834:Chaperonin 60; D003374:Coumarins; D046912:Multiprotein Complexes; D028044:Phosphate-Binding Proteins; C088410:N-(2-(1-maleimidyl)ethyl)-7-(diethylamino)coumarin-3-carboxamide; D000255:Adenosine Triphosphate; D007768:Lactalbumin