A thermodynamic coupling mechanism for GroEL-mediated unfolding

被引:100
作者
Walter, S
Lorimer, GH
Schmid, FX
机构
[1] UNIV BAYREUTH,BIOCHEM LAB,D-95440 BAYREUTH,GERMANY
[2] DUPONT CO INC,DEPT CENT RES & DEV,EXPT STN,WILMINGTON,DE 19880
关键词
protein folding; chaperones; heat shock proteins; folding kinetics; RNase T1;
D O I
10.1073/pnas.93.18.9425
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Chaperonins prevent the aggregation of partially folded or misfolded forms of a protein and, thus, keep it competent for productive folding. It was suggested that GroEL, the chaperonin of Escherichia coli, exerts this function by unfolding such intermediates, presumably in a catalytic fashion. We investigated the kinetic mechanism of GroEL-induced protein unfolding by using a reduced and carbamidomethylated variant of RNase T1, RCAM-T1, as a substrate. RCAM-T1 cannot fold to completion, because the two disulfide bonds are missing, and it is, thus, a good model for long-lived folding intermediates. RCAM-T1 unfolds when GroEL is added, but GroEL does not change the microscopic rate constant of unfolding, ruling out that it catalyzes unfolding. GroEL unfolds RCAM-T1 because it binds with high affinity to the unfolded form of the protein and thereby shifts the overall equilibrium toward the unfolded state. GroEL can unfold a partially folded or misfolded intermediate by this thermodynamic coupling mechanism when the Gibbs free energy of the binding to GroEL is larger than the conformational stability of the intermediate and when the rate of its unfolding is high.
引用
收藏
页码:9425 / 9430
页数:6
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