TitleModulation of the Extent of Cooperative Structural Change During Protein Folding by Chemical Denaturant.
Publication TypeJournal Article
Year of Publication2017
AuthorsJethva PN, Udgaonkar JB
JournalJ Phys Chem B
Volume121
Issue35
Pagination8263-8275
Date Published2017 Sep 07
ISSN1520-5207
Abstract

Protein folding and unfolding reactions invariably appear to be highly cooperative reactions, but the structural and sequence determinants of cooperativity are poorly understood. Importantly, it is not known whether cooperative structural change occurs throughout the protein, or whether some parts change cooperatively and other parts change noncooperatively. In the current study, hydrogen exchange mass spectrometry has been used to show that the mechanism of unfolding of the PI3K SH3 domain is similar in the absence and presence of 5 M urea. The data are well described by a four state N ↔ IN ↔ I2 ↔ U model, in which structural changes occur noncooperatively during the N ↔ IN and IN ↔ I2 transitions, and occur cooperatively during the I2 ↔ U transition. The nSrc-loop and RT-loop, as well as β strands 4 and 5 undergo noncooperative unfolding, while β strands 1, 2, and 3 unfold cooperatively in the absence of urea. However, in the presence of 5 M urea, the unfolding of β strand 4 switches to become cooperative, leading to an increase in the extent of cooperative structural change. The current study highlights the relationship between protein stability and cooperativity, by showing how the extent of cooperativity can be varied, using chemical denaturant to alter protein stability.

DOI10.1021/acs.jpcb.7b04473
Alternate JournalJ Phys Chem B
PubMed ID28771359