Title
Hydrophobic Collapse of Ubiquitin Generates Rapid Protein–Water Motions
Author
Hanna Wirtz, Sarah Schäfer, Claudius Hoberg, Korey M. Reid, David M. Leitner, Martina Havenith
Year
2018
Journal
Biochemistry
Abstract
We report time-resolved measurements of the coupled protein–water modes of solvated ubiquitin during protein folding. Kinetic terahertz absorption (KITA) spectroscopy serves as a label-free technique for monitoring large scale conformational changes and folding of proteins subsequent to a sudden T-jump. We report here KITA measurements at an unprecedented time resolution of 500 ns, a resolution 2 orders of magnitude better than those of any previous KITA measurements, which reveal the coupled ubiquitin–solvent dynamics even in the initial phase of hydrophobic collapse. Complementary equilibrium experiments and molecular simulations of ubiquitin solutions are performed to clarify non-equilibrium contributions and reveal the molecular picture upon a change in structure, respectively. On the basis of our results, we propose that in the case of ubiquitin a rapid (<500 ns) initial phase of the hydrophobic collapse from the elongated protein to a molten globule structure precedes secondary structure formation. We find that these very first steps, including large-amplitude changes within the unfolded manifold, are accompanied by a rapid (<500 ns) pronounced change of the coupled protein–solvent response. The KITA response upon secondary structure formation exhibits an opposite sign, which indicates a distinct effect on the solvent-exposed surface.
Instrument
J-715
Keywords
Circular dichroism, Secondary structure, Protein folding, Thermal stability, Thermodynamics, Biochemistry