The inverted chevron plot measured by NMR relaxation reveals a native-like unfolding intermediate in acyl-CoA binding protein.

TY - JOUR

T1 - The inverted chevron plot measured by NMR relaxation reveals a native-like unfolding intermediate in acyl-CoA binding protein.

AU - Teilum, Kaare

AU - Poulsen, F. M.

AU - Akke, M.

PY - 2006

Y1 - 2006

N2 - The folding kinetics of bovine acyl-CoA binding protein was studied by 15N relaxation dispersion measurements under equilibrium conditions. Relaxation dispersion profiles were measured at several concentrations of guanidine hydrochloride (GuHCl). The unfolding rate constant (k u) was determined under conditions favoring folding, for which the folding rate constant (k f) dominates the relaxation in stopped-flow kinetic measurements. Conversely, k f was determined under conditions favoring unfolding, for which k u dominates stopped-flow data. The rates determined by NMR therefore complement those from stopped-flow kinetics and define an "inverted chevron" plot. The combination of NMR relaxation and stopped-flow kinetic measurements allowed determination of k f and k u in the range from 0.48 M GuHCl to 1.28 M GuHCl. Individually, the stopped-flow and NMR data fit two-state models for folding. However, although the values of k f determined by the two methods agree, the values of k u do not. As a result, a combined analysis of all data does not comply with a two-state model but indicates that an unfolding intermediate exists on the native side of the dominant energy barrier. The denaturant and temperature dependencies of the chemical shifts and k u indicate that the intermediate state is structurally similar to the native state. Equilibrium unfolding monitored by optical spectroscopy corroborate these conclusions. The temperature dependence of the chemical shifts identifies regions of the protein that are selectively destabilized in the intermediate. These results illustrate the power of combining stopped-flow kinetics and NMR spectroscopy to analyze protein folding.

AB - The folding kinetics of bovine acyl-CoA binding protein was studied by 15N relaxation dispersion measurements under equilibrium conditions. Relaxation dispersion profiles were measured at several concentrations of guanidine hydrochloride (GuHCl). The unfolding rate constant (k u) was determined under conditions favoring folding, for which the folding rate constant (k f) dominates the relaxation in stopped-flow kinetic measurements. Conversely, k f was determined under conditions favoring unfolding, for which k u dominates stopped-flow data. The rates determined by NMR therefore complement those from stopped-flow kinetics and define an "inverted chevron" plot. The combination of NMR relaxation and stopped-flow kinetic measurements allowed determination of k f and k u in the range from 0.48 M GuHCl to 1.28 M GuHCl. Individually, the stopped-flow and NMR data fit two-state models for folding. However, although the values of k f determined by the two methods agree, the values of k u do not. As a result, a combined analysis of all data does not comply with a two-state model but indicates that an unfolding intermediate exists on the native side of the dominant energy barrier. The denaturant and temperature dependencies of the chemical shifts and k u indicate that the intermediate state is structurally similar to the native state. Equilibrium unfolding monitored by optical spectroscopy corroborate these conclusions. The temperature dependence of the chemical shifts identifies regions of the protein that are selectively destabilized in the intermediate. These results illustrate the power of combining stopped-flow kinetics and NMR spectroscopy to analyze protein folding.

M3 - Journal article

SN - 0027-8424

VL - 103

SP - 6867

EP - 6882

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 18

ER -