title: The major transition state in folding need not involve the immobilization of side chains.
abstract: During protein folding in which few, if any, definable kinetic intermediates are observable, the nature of the transition state is central to understanding the course of the reaction. Current experimental data does not distinguish the relative contributions of side chain immobilization and dehydration phenomena to the major rate-limiting transition state whereas this distinction is central to theoretical models that attempt to simulate the behavior of proteins during folding. Renaturation of the small proteinase inhibitor cystatin under oxidizing versus reducing conditions is the first experimental case in which these processes can be studied independently. Using this example, we show that sidechain immobilization occurs downstream of the major folding transition state. A consequence of this is the existence of states with disordered side chains, which are distinct from kinetic protein folding intermediates and which lie within the folded state free energy well.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom. r.a.staniforth@sheffield.ac.uk
authors.forename: R A
authors.initials: RA
authors.lastname: Staniforth
authors.forename: J L
authors.initials: JL
authors.lastname: Dean
authors.forename: Q
authors.initials: Q
authors.lastname: Zhong
authors.forename: E
authors.initials: E
authors.lastname: Zerovnik
authors.forename: A R
authors.initials: AR
authors.lastname: Clarke
authors.forename: J P
authors.initials: JP
authors.lastname: Waltho
mesh_terms: D000818:Animals; D002645:Chickens; D002942:Circular Dichroism; D015891:Cystatins / Q000737:chemistry; D003553:Cystine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D015891:Cystatins; D011993:Recombinant Fusion Proteins; D003553:Cystine