T. Zinkevich, V. Chevelkov, B. Reif, K. Saalwächter, A. Krushelnitsky.
Internal protein dynamics on ps to us timescales as studied
by multi-frequency 15N solid-state NMR relaxation.
J. Biomol. NMR 57, 219-235 (2013).
A comprehensive analysis of the dynamics of
the SH3 domain of chicken alpha-spectrin is presented,
based upon 15N T1 and on- and off-resonance T1ρ relaxation
times obtained on deuterated samples with a partial
back-exchange of labile protons under a variety of the
experimental conditions, taking explicitly into account the
dipolar order parameters calculated from 15N–1H dipole–
dipole couplings. It is demonstrated that such a multi-frequency
approach enables access to motional correlation
times spanning about 6 orders of magnitude. We asses the
validity of different motional models based upon orientation
autocorrelation functions with a different number of
motional components. We find that for many residues a
‘‘two components’’ model is not sufficient for a good
description of the data and more complicated fitting models
must be considered. We show that slow motions with
correlation times on the order of 1–10 μs can be determined
reliably in spite of rather low apparent amplitudes
(below 1 %), and demonstrate that the distribution
of the protein backbone mobility along the time scale
axis is pronouncedly non-uniform and non-monotonic:
two domains of fast (s < 10-10 s) and intermediate
(10-9 s < τ < 10-7 s) motions are separated by a gap of
one order of magnitude in time with almost no motions.
For slower motions (s < 10-6 s) we observe a sharp *1
order of magnitude decrease of the apparent motional
amplitudes. Such a distribution obviously reflects different
nature of backbone motions on different time scales, where
the slow end may be attributed to weakly populated
‘‘excited states.’’ Surprisingly, our data reveal no clearly
evident correlations between secondary structure of the
protein and motional parameters. We also could not notice
any unambiguous correlations between motions in different
time scales along the protein backbone emphasizing the
importance of the inter-residue interactions and the cooperative
nature of protein dynamics.