Urea, but not guanidinium, destabilizes proteins by forming hydrogen bonds to the peptide group
- aDepartment of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104;
- bDepartment of Molecular Biology, College of Natural Sciences, Pusan National University, Jangjeon-dong, Keumjeong District, Busan 609-735, South Korea; and
- cDepartment of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555
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Contributed by S. Walter Englander, December 10, 2008 (received for review November 25, 2008)

Abstract
The mechanism by which urea and guanidinium destabilize protein structure is controversial. We tested the possibility that these denaturants form hydrogen bonds with peptide groups by measuring their ability to block acid- and base-catalyzed peptide hydrogen exchange. The peptide hydrogen bonding found appears sufficient to explain the thermodynamic denaturing effect of urea. Results for guanidinium, however, are contrary to the expectation that it might H-bond. Evidently, urea and guanidinium, although structurally similar, denature proteins by different mechanisms.
Footnotes
- 1To whom correspondence may be addressed. E-mail: jorosgen{at}utmb.edu or engl{at}mail.med.upenn.edu
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Author contributions: W.K.L., J.R., and S.W.E. designed research; W.K.L. performed research; W.K.L. and J.R. analyzed data; and J.R. and S.W.E. wrote the paper.
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The authors declare no conflict of interest.
- © 2009 by The National Academy of Sciences of the USA
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