Two-state folding over a weak free-energy barrier

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Abstract

We present a Monte Carlo study of a model protein with 54 amino acids that folds directly to its native three-helix-bundle state without forming any well-defined intermediate state. The free-energy barrier separating the native and unfolded states of this protein is found to be weak, even at the folding temperature. Nevertheless, we find that melting curves to a good approximation can be described in terms of a simple two-state system, and that the relaxation behavior is close to single exponential. The motion along individual reaction coordinates is roughly diffusive on timescales beyond the reconfiguration time for a single helix. A simple estimate based on diffusion in a square-well potential predicts the relaxation time within a factor of two.

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  • Biophysics
Original languageEnglish
Pages (from-to)1457-1465
JournalBiophysical Journal
Volume85
Issue number3
Publication statusPublished - 2003
Publication categoryResearch
Peer-reviewedYes