Enthalpic Barriers Dominate the Folding and Unfolding of the Human Cu, Zn Superoxide Dismutase Monomer

JOURNAL OF MOLECULAR BIOLOGY

卷:424

Article

Kayatekin, Can¹  Cohen, Noah R.¹  Matthews, C. Robert¹ 

[1] Univ Massachusetts, Sch Med, Dept Biochem & Mol Pharmacol, Worcester, MA 01605 USA

关键词: protein folding;    enthalpy;    entropy;    heat capacity;    enthalpy/entropy compensation;   

DOI  :  10.1016/j.jmb.2012.09.009

来源: Elsevier

【 摘 要 】

The rate-limiting step in the formation of the native dimeric state of human Cu, Zn superoxide dismutase (SOD1) is a very slow monomer folding reaction that governs the lifetime of its unfolded state. Mutations at dozens of sites in SOD1 are known to cause a fatal motor neuron disease, amyotrophic lateral sclerosis, and recent experiments implicate the unfolded state as a source of soluble oligomers and histologically observable aggregates thought to be responsible for toxicity. To determine the thermodynamic properties of the transition state ensemble (TSE) limiting the folding of this high-contact-order beta-sandwich motif, we performed a combined thermal/urea denaturation thermodynamic/kinetic analysis. The barriers to folding and unfolding are dominated by the activation enthalpy at 298 K and neutral pH; the activation entropy is favorable and reduces the barrier height for both reactions. The absence of secondary structure formation or large-scale chain collapse prior to crossing the barrier for folding led to the conclusion that dehydration of nonpolar surfaces in the TSE is responsible for the large and positive activation enthalpy. Although the activation entropy favors the folding reaction, the transition from the unfolded state to the native state is entropically disfavored at 298K. The opposing entropic contributions to the free energies of the TSE and the native state during folding provide insights into structural properties of the TSE. The results also imply a crucial role for water in governing the productive folding reaction and enhancing the propensity for the aggregation of SOD1. (C) 2012 Elsevier Ltd. All rights reserved.

【 授权许可】

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