Spectrin R16: Broad energy barrier or sequential transition states?

• Published in: Protein science Vol. 14; no. 6; pp. 1617 - 1629
• Main Authors: Scott, Kathryn A., Clarke, Jane
• Format: Journal Article
• Language: English
• Published: Bristol Cold Spring Harbor Laboratory Press 01.06.2005
• Subjects: Animals; chevron plot; curvature; Humans; Protein Denaturation; Protein Folding; Protein Structure, Secondary; spectrin; Spectrin - chemistry; Thermodynamics; transition states; Φ‐value
• ISSN: 0961-8368; 1469-896X
• DOI: 10.1110/ps.051377105

A number of models have been proposed to account for nonlinearity in the relation between observed rate constants for folding and/or unfolding and denaturant concentration. Where curvature is seen principally in the arm of a chevron plot, three explanations are proposed: a change in the ground state at increasing concentration of urea, movement of the transition state along a broad energy barrier, and a switch between two sequential transition states separated by an on‐pathway high‐energy intermediate. Here we demonstrate that the latter two models in particular can be used to describe the data for the all‐α protein spectrin R16. Further, whatever the method of analysis, the pattern of Φ‐values seen is robust; thus we would draw the same conclusions from our data set independently of the method used for analysis. While this is not a novel observation, this is the first systematic study where a comparison has been made between Φ‐values calculated using the broad and sequential transition state models.