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Published online before print April 9, 2004, 10.1110/ps.03559504
Protein Science (2004), 13:1317-1321. Published by Cold Spring Harbor Laboratory Press. Copyright © 2004 The Protein Society
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Monomer topology defines folding speed of heptamer

Neil Bascos1, Jesse Guidry2 and Pernilla Wittung-Stafshede3

1 Molecular and Cellular Biology Graduate Program, Tulane University, New Orleans, Louisiana 70112, USA
2 Louisiana State University Health Science Center, Department of Pharmacology, New Orleans, Louisiana 70112, USA
3 Biochemistry and Cell Biology and Chemistry Departments, Rice University, Houston, Texas 77251, USA

(RECEIVED December 9, 2003; FINAL REVISION January 27, 2004; ACCEPTED January 27, 2004)



Abstract

Small monomeric proteins often fold in apparent two-state processes with folding speeds dictated by their native-state topology. Here we test, for the first time, the influence of monomer topology on the folding speed of an oligomeric protein: the heptameric cochaperonin protein 10 (cpn10), which in the native state has seven {beta}-barrel subunits noncovalently assembled through {beta}-strand pairing. Cpn10 is a particularly useful model because equilibrium-unfolding experiments have revealed that the denatured state in urea is that of a nonnative heptamer. Surprisingly, refolding of the nonnative cpn10 heptamer is a simple two-state kinetic process with a folding-rate constant in water (2.1 sec–1; pH 7.0, 20°C) that is in excellent agreement with the prediction based on the native-state topology of the cpn10 monomer. Thus, the monomers appear to fold as independent units, with a speed that correlates with topology, although the C and N termini are trapped in {beta}-strand pairing with neighboring subunits. In contrast, refolding of unfolded cpn10 monomers is dominated by a slow association step.

Keywords: cochaperonin protein; protein folding; protein assembly; contact order; topology

Reprint requests to: Pernilla Wittung-Stafshede, Biochemistry and Cell Biology Department, MS-140, Rice University, Houston, TX 77251, USA; e-mail: pernilla{at}rice.edu (713) 348-5154.

Article published ahead of print. Article and publication date are at http://www.proteinscience.org/cgi/doi/10.1110/ps.03559504.


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