Conformational changes during the nanosecond-to-millisecond unfolding of ubiquitin

被引:131
作者
Chung, HS [1 ]
Khalil, M [1 ]
Smith, AW [1 ]
Ganim, Z [1 ]
Tokmakoff, A [1 ]
机构
[1] MIT, Dept Chem, Cambridge, MA 02139 USA
关键词
protein-folding dynamics; temperature jump; nonlinear IR spectroscopy;
D O I
10.1073/pnas.0408646102
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Steady-state and transient conformational changes upon the thermal unfolding of ubiquitin were investigated with nonlinear IR spectroscopy of the amide I vibrations. Equilibrium temperaturedependent 2D IR spectroscopy reveals the unfolding of the beta-sheet of ubiquitin through the loss of cross peaks formed between transitions arising from delocalized vibrations of the beta-sheet. Transient unfolding after a nanosecond temperature jump is monitored with dispersed vibrational echo spectroscopy, a projection of the 2D IR spectrum. Whereas the equilibrium study follows a simple two-state unfolding, the transient experiments observe complex relaxation behavior that differs for various spectral components and spans 6 decades in time. The transient behavior can be separated into fast and slow time scales. From 100 ns to 0.5 ms, the spectral features associated with p-sheet unfolding relax in a sequential, nonexponential manner, with time constants of 3 mus and 80 mus. By modeling the amide I vibrations of ubiquitin, this observation is explained as unfolding of the less stable strands lll-V of the beta-sheet before unfolding of the hairpin that forms part of the hydrophobic core. This downhill unfolding is followed by exponential barrier-crossing kinetics on a 3-ms time scale.
引用
收藏
页码:612 / 617
页数:6
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