title: Restricted diffusion of methyl groups in proteins revealed by deuteron NMR: manifestation of intra-well dynamics.
abstract: The three-site hops of methyl groups are usually used as an approximation of the mechanistic description of motions responsible for the longitudinal NMR relaxation. Distinguishing between three-site hops and a more realistic mechanism of diffusion in a potential requires extended experimental and computational analysis. In order to achieve this goal, in this work the restricted diffusion is decomposed into two independent modes, namely, the jumps between potential wells and intra-well fluctuations, assuming time scale separation between these modes. This approach allows us to explain the rise in the theoretical value of T1 minimum for the restricted diffusion mechanism compared with the three-site hops mechanism via rescaling the three-site hops correlation function by the order parameter of intra-well motions. The main result of the paper is that, in general, intra-well dynamics can be visible in NMR even in the limit of large barrier heights in contrast to the common view that this limit converges to the three-site hops mechanism. Based on a previously collected detailed set of deuteron NMR relaxation and spectral data in the villin headpiece subdomain protein over a wide temperature range of 300-31 K, we are then able to conclude that the mechanism of diffusion in the threefold potential is likely to be the main source of the dynamics in this system.
authors.affiliation: Department of Chemistry, University of Alaska Anchorage, Anchorage, Alaska 99508, USA.
authors.forename: Liliya
authors.initials: L
authors.lastname: Vugmeyster
authors.affiliation: Department of Mathematics, University of Alaska Anchorage, Anchorage, Alaska 99508, USA.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Ostrovsky
mesh_terms: D003903:Deuterium / Q000032:analysis; D004058:Diffusion; D008745:Methylation; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011506:Proteins / Q000737:chemistry*
chemical_list: D011506:Proteins; D003903:Deuterium