Journal
PROTEIN SCIENCE
Volume 13, Issue 5, Pages 1317-1321Publisher
WILEY
DOI: 10.1110/ps.03559504
Keywords
cochaperonin protein; protein folding; protein assembly; contact order; topology
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Funding
- NIGMS NIH HHS [GM59663, R01 GM059663] Funding Source: Medline
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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 (cpn 10), 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 normative heptamer. Surprisingly, refolding of the normative cpn 10 heptamer is a simple two-state kinetic process with a folding-rate constant in water (2.1 sec(-1); pH 7.0, 20degreesC) 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.
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