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Backbone motions in a crystalline protein from field‐dependent 2 H‐NMR relaxation and line‐shape analysis
Author(s) -
Mack James W.,
Usha M. G.,
Long Joanna,
Griffin Robert G.,
Wittebort R. J.
Publication year - 2000
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/(sici)1097-0282(200001)53:1<9::aid-bip2>3.0.co;2-6
Subject(s) - chemistry , relaxation (psychology) , microsecond , nmr spectra database , amplitude , spin–lattice relaxation , transverse relaxation optimized spectroscopy , nuclear magnetic resonance spectroscopy , quadrupole , nuclear magnetic resonance , proton nmr , molecular physics , analytical chemistry (journal) , spectral line , atomic physics , nuclear quadrupole resonance , stereochemistry , fluorine 19 nmr , physics , psychology , social psychology , quantum mechanics , astronomy , chromatography
We have used 2 H‐nmr to study backbone dynamics of the 2 H‐labeled, slowly exchanging amide sites of fully hydrated, crystalline hen egg white lysozyme. Order parameters are determined from the residual quadrupole coupling and values increase from S 2 = 0.85 at 290 K to S 2 = 0.94 at 200 K. Dynamical rates are determined from spin–lattice relaxation at three nmr frequencies (38.8, 61.5, and 76.7 MHz). The approach used here is thus distinct from solution nmr studies where dynamical amplitudes and rates are both determined from relaxation measurements. At temperatures below 250 K, relaxation is independent of the nmr frequency indicating that backbone motions are fast compared to the nmr frequencies. However, as the temperature is increased above 250 K, relaxation is significantly more efficient at the lowest frequency, which shows, in addition, the presence of motions that are slow compared to the nmr frequencies. Using the values of S 2 determined from the residual quadrupole coupling and a model‐free relaxation formalism that allows for fast and slow internal motions, we conclude that these slow motions have correlation times in the range of 0.1 to 1.0 μs and are effectively frozen out at 250 K where fast motions of the amide planes with ∼ 15 ps effective correlation times and 9° rms amplitudes dominate relaxation. The fast internal motions increase slightly in amplitude as the temperature rises toward 290 K, but the correlation time, as is also observed in solution nmr studies of RNase H, is approximately constant. These findings are consistent with hypotheses of dynamic glass transitions in hydrated proteins arising from temperature‐dependent damping of harmonic modes of motion above the transition point. © 2000 John Wiley & Sons, Inc. Biopoly 53: 9–18, 2000