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Solvent‐tuning the collapse and helix formation time scales of λ 6‐85 *
Author(s) -
Dumont Charles,
Matsumura Yoshitaka,
Kim Seung Joong,
Li Jinsong,
Kondrashkina Elena,
Kihara Hiroshi,
Gruebele Martin
Publication year - 2006
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.062257406
Subject(s) - radius of gyration , chemistry , downhill folding , folding (dsp implementation) , kinetics , protein folding , helix (gastropod) , circular dichroism , guanidine , crystallography , hydrodynamic radius , ethylene glycol , aqueous solution , solvent , chemical physics , protein secondary structure , phi value analysis , physics , polymer , organic chemistry , ecology , biochemistry , quantum mechanics , snail , electrical engineering , biology , engineering , micelle
The λ 6‐85 * pseudo‐wild type of lambda repressor fragment is a fast two‐state folder ( k f ≈ 35 μsec −1 at 58°C). Previously, highly stable λ 6‐85 * mutants with k f > 30 μsec −1 have been engineered to fold nearly or fully downhill. Stabilization of the native state by solvent tuning might also tune λ 6‐85 * away from two‐state folding. We test this prediction by examining the folding thermodynamics and kinetics of λ 6‐85 * in a stabilizing solvent, 45% by weight aqueous ethylene glycol at −28°C. Detection of kinetics by circular dichroism at 222 nm (sensitive to helix content) and small angle X‐ray scattering (measuring the radius of gyration) shows that refolding from guanidine hydrochloride denatured conditions exhibits very different time scales for collapse and secondary structure formation: the two processes become decoupled. Collapse remains a low‐barrier activated process, while the fastest of several secondary structure formation time scales approaches the downhill folding limit. Two‐state folding of λ 6‐85 * is not a robust process.