Dynamics and Chemical Shielding in a Small Protein from NMR Spin Relaxation Experiments

Abstract

NMR spin relaxation spectroscopy is a proven method for characterization of the time-scales and amplitudes of intramolecular motions in proteins. In a typical NMR relaxation experiment, the significant contributions to relaxation of the 15N spin are from the 1H-15N dipolar interaction with the covalently attached amide proton and from the anisotropic component of the 15N chemical shielding tensor, the 15N chemical shielding anisotropy (CSA). Herein I suggest novel schemes for the measurement of CSA/dipolar cross-correlation rates in proteins and for direct nitrogen-detected relaxation measurements. I also conduct a series of established NMR 15N spin relaxation experiments on a small protein, the B3 domain of Streptococcal protein G, in order to measure the overall rotational diffusion tensor of this domain, to quantify any conformational exchange type motion of backbone amides occurring in this protein on the s-ms timescale, and to determine the 15N backbone amide CSAs in this protein in solution and quantify the effect of residue-to-residue variations in the 15N CSA on model-free motional parameters which describe motions on the ps-ns timescale.