Abstract
Despite extensive efforts in experimental and computational studies, the microscopic understanding of dynamics of biological macromolecules remains a great challenge. It is known that hydrated proteins, DNA and RNA, exhibit a so-called "dynamic transition." It appears as a sharp rise of their mean-squared atomic displacements 〈 r2 〉 at temperatures above 200-230 K. Even after a long history of studies, this sudden activation of biomolecular dynamics remains a puzzle and many contradicting models have been proposed. By combining neutron and dielectric spectroscopy data, we were able to follow protein dynamics over an extremely broad frequency range. Our results show that there is no sudden change in the dynamics of the protein at temperatures around ∼200-230 K. The protein's relaxation time exhibits a smooth temperature variation over the temperature range of 180-300 K. Thus the experimentally observed sharp rise in 〈 r2 〉 is just a result of the protein's structural relaxation reaching the limit of the experimental frequency window. The microscopic mechanism of the protein's structural relaxation remains unclear.
Original language | English |
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Article number | 195106 |
Journal | Journal of Chemical Physics |
Volume | 128 |
Issue number | 19 |
DOIs | |
State | Published - 2008 |
Externally published | Yes |
Funding
The Akron team acknowledges financial support from NSF Polymer program. This work utilized facilities supported in part by NSF under Agreement No. DMR-0454672. We acknowledge the support of ORNL and of NIST Center for Neutron Research in providing the neutron research facilities used in this work. A portion of this research at ORNL's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.