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Free keywords:
Cryo-probe; Protein dynamics; Rotating-frame transverse relaxation;
Relaxation dispersion; Ubiquitin
Abstract:
Internal motions in the microsecond timescale have been proposed to play an active part in a protein’s
biological function. Nuclear magnetic resonance (NMR) relaxation dispersion is a robust method sensitive
to this timescale with atomic resolution. However, due to technical limitations, the observation of
motions faster than
40
l
s for
15
N nuclei was not possible. We show that with a cryogenically cooled
NMR probehead, a high spin-lock field strength can be generated that is able to detect motions as fast
as 25
l
s. We apply this high spin-lock field strength in an NMR experiment used for characterizing
dynamical processes. An on-resonance rotating-frame transverse relaxation experiment was imple-
mented that allows for the detection of a 25
l
s process from a dispersion curve, and transverse relaxation
rates were compared at low and high spin-lock field strengths showing that at high field strengths con-
tributions from chemical exchange with lifetimes up to 25
l
s can be removed. Due to the increase in sen-
sitivity towards fast motion, relaxation dispersion for a residue that undergoes smaller chemical shift
variations due to dynamics was identified. This technique reduces the previously inaccessible window
between the correlation time and the relaxation dispersion window that covers four orders of magnitude
by a factor of 2.
