Anatomy of energetic changes accompanying urea-induced protein denaturation

Matthew Auton, Luis Marcelo F. Holthauzen, D. Wayne Bolen

Research output: Contribution to journalArticle

214 Scopus citations

Abstract

Because of its protein-denaturing ability, urea has played a pivotal role in the experimental and conceptual understanding of protein folding and unfolding. The measure of urea's ability to force a protein to unfold is given by the m value, an experimental quantity giving the free energy change for unfolding per molar urea. With the aid of Tanford's transfer model [Tanford C (1964) J Am Chem Soc 86:2050-2059], we use newly obtained group transfer free energies (GTFEs) of protein side-chain and backbone units from water to 1 M urea to account for the m value of urea, and the method reveals the anatomy of protein denaturation in terms of residue-level free energy contributions of groups newly exposed on denaturation. The GTFEs were obtained by accounting for solubility and activity coefficient ratios accompanying the transfer of glycine from water to 1 M urea. Contrary to the opinions of some researchers, the GTFEs show that urea does not denature proteins through favorable interactions with nonpolar side chains; what drives urea-induced protein unfolding is the large favorable interaction of urea with the peptide backbone. Although the m value is said to be proportional to surface area newly exposed on denaturation, only ≈25% of the area favorably contributes to unfolding (because of newly exposed backbone units), with ≈75% modestly opposing urea-induced denaturation (originating from side-chain exposure). Use of the transfer model and newly determined GTFEs achieves the long-sought goal of predicting urea-dependent cooperative protein unfolding energetics at the level of individual amino acid residues.

Original languageEnglish (US)
Pages (from-to)15317-15322
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume104
Issue number39
DOIs
StatePublished - Sep 25 2007

Keywords

  • Activity coefficient
  • M value
  • Self-avoiding random coil
  • Transfer free energy
  • Transfer model

ASJC Scopus subject areas

  • General

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