Solvent-tuning the collapse and helix formation time scales of λ6-85*

Charles Dumont, Yoshitaka Matsumura, Joong Kim Seung, Jinsong Li, Elena Kondrashkina, Hiroshi Kihara, Martin Gruebele

Research output: Contribution to journalArticlepeer-review


The λ6-85* pseudo-wild type of lambda repressor fragment is a fast two-state folder (kf ≈ 35 μsec-1 at 58°C). Previously, highly stable λ6-85* mutants with kf > 30 μsec-1 have been engineered to fold nearly or fully downhill. Stabilization of the native state by solvent tuning might also tune λ6-85* away from two-state folding. We test this prediction by examining the folding thermodynamics and kinetics of λ6-85* 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 λ6-85* is not a robust process. Published by Cold Spring Harbor Laboratory Press.

Original languageEnglish (US)
Pages (from-to)2596-2604
Number of pages9
JournalProtein Science
Issue number11
StatePublished - 2006


  • Collapse
  • Cryosolvent
  • Heterogeneous kinetics
  • Stopped flow

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology


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