Hydrogen exchange, protein unfolding

Amide proton temperature coefficients and hydrogen exchange rates can provide information about hydrogen-bonding interactions and solvent sequestration in unfolded or partly folded proteins (Dyson and Wright, 1991). Abnormally low temperature coefficients, relative to random coil values, are a clear indication of local structure and interactions. 

Amide hydrogen exchange is usually discussed in terms of a model proposed by Linderstrc )m-Lang in 1955.554/556 He suggested that portions of protein molecules unfold sporadically to allow rapid exchange which can be catalyzed by H+, HO, or other acids or... 

Other measures of protein flexibility have been found to correlate with thermal stability. One is resistance to proteolysis (Daniel et al., 1982 Fontana, 1988). Another is the quenching of buried tryptophan fluorescence by acrylamide, used in a study by Varley and Pain (1991). Both these processes are mediated by the same combination of local and global unfolding events that determine rates of hydrogen exchange. Their rates will depend on the ability of another molecule, acrylamide or a proteolytic enzyme, to penetrate into normally buried regions of the protein in order to either quench fluorescence or cleave peptide bonds. 

Hydrogen exchange of a protein under denaturing conditions can be described by the following simple two-state (folded/unfolded) model ... 

The model simply proposes that hydrogen exchange may occur (with different rates) in both the folded and unfolded forms of the protein, and that the folding/unfolding rates are not affected by replacement of amide hydrogens by deuteriums. (Note that experiments in D2O, since there are no... 

Detection of protein unfolding and fluctuations by native state hydrogen exchange... 

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