GSBS Student Publications

Title

Microsecond barrier-limited chain collapse observed by time-resolved FRET and SAXS

Student Author(s)

R. Paul Nobrega

GSBS Program

Biochemistry & Molecular Pharmacology

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology

Date

5-1-2014

Document Type

Article

Disciplines

Molecular Biology

Abstract

It is generally held that random-coil polypeptide chains undergo a barrier-less continuous collapse when the solvent conditions are changed to favor the fully folded native conformation. We test this hypothesis by probing intramolecular distance distributions during folding in one of the paradigms of folding reactions, that of cytochrome c. The Trp59-to-heme distance was probed by time-resolved Forster resonance energy transfer in the microsecond time range of refolding. Contrary to expectation, a state with a Trp59-heme distance close to that of the guanidinium hydrochloride (GdnHCl) denatured state is present after ~27 mus of folding. A concomitant decrease in the population of this state and an increase in the population of a compact high-FRET (Forster resonance energy transfer) state (efficiency > 90%) show that the collapse is barrier limited. Small-angle X-ray scattering (SAXS) measurements over a similar time range show that the radius of gyration under native favoring conditions is comparable to that of the GdnHCl denatured unfolded state. An independent comprehensive global thermodynamic analysis reveals that marginally stable partially folded structures are also present in the nominally unfolded GdnHCl denatured state. These observations suggest that specifically collapsed intermediate structures with low stability in rapid equilibrium with the unfolded state may contribute to the apparent chain contraction observed in previous fluorescence studies using steady-state detection. In the absence of significant dynamic averaging of marginally stable partially folded states and with the use of probes sensitive to distance distributions, barrier-limited chain contraction is observed upon transfer of the GdnHCl denatured state ensemble to native-like conditions.

DOI of Published Version

10.1016/j.jmb.2014.02.020

Source

J Mol Biol. 2014 May 1;426(9):1980-94. doi: 10.1016/j.jmb.2014.02.020. Epub 2014 Mar 4. Link to article on publisher's site

Related Resources

Link to Article in PubMed

Journal Title

Journal of molecular biology

PubMed ID

24607691

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