Temperature dependence of fast dynamics in proteins

¹ University of Pennsylvania
² University of Utah

^* To whom correspondence should be addressed. E-mail: wand{at}mail.med.upenn.edu.

Submitted on November 30, 2006
Revised on December 10, 2006
Accepted on 3 January 2007

	Abstract

The temperature dependence of the internal dynamics of recombinant human ubiquitin has been measured using solution NMR relaxation techniques. Nitrogen-15 relaxation has been employed to obtain a measure of the amplitude of sub-nanosecond motion at amide N-H sites in the protein. Deuterium relaxation has been used to obtain a measure of the amplitude of motion of methyl-groups in amino acid side chains. Data was obtained between 5 and 55° C. The majority of amide N-H and methyl groups show a roughly linear (R² > 0.75) temperature dependence of the associated Lipari-Szabo model-free squared generalized order parameter (O²) describing the amplitude of motion. Interestingly, for those sites showing a linear response, the temperature dependence of the backbone is distinct from that of the methyl-bearing side chains with the former being characterized by a significantly larger value, where is defined as d ln(1-O)/ d lnT. These results are comparable to the sole previous such study of the temperature dependence of protein motion obtained for a calmodulin-peptide complex. This suggests that the distinction between the main chain and methyl-bearing side chains may be general. Insight into the temperature dependence is gathered from a simple two-state step potential model.

Key Words: NMR relaxation, protein dynamics, side chain motion, ubiquitin