Magic-Angle-Pulse Driven Separation of Degenerate 1 H Transitions in Methyl Groups of Proteins: Application to Studies of Methyl Axis Dynamics

Abstract

Dynamics of protein side chains is one of the principal determinants of conformational entropy in protein structures and molecular recognition events. We describe NMR experiments that rely on the use of magic-angle pulses for efficient isolation of degenerate ¹ H transitions of the I=3/2 manifold of ¹³ CH₃ methyl groups, and serve as 'building blocks' for the measurement of transverse spin relaxation rates of the fast- and slow-relaxing ¹ H transitions - the primary quantitative reporters of methyl axis dynamics in selectively {¹³ CH₃ }-methyl-labelled, highly deuterated proteins. The magic-angle-pulse driven experiments are technically simpler and, in the absence of relaxation, predicted to be 2.3-fold more sensitive than previously developed analogous schemes. Validation of the methodology on a sample of {¹³ CH₃ }-labeled ubiquitin demonstrates quantitative agreement between order parameters of methyl three-fold symmetry axis obtained with magic-angle-pulse driven experiments and other established NMR techniques, paving the way for studies of methyl axis dynamics in human DNAJB6b chaperone, a protein that undergoes exchange with high-molecular-weight oligomeric species.

Keywords: 13CH3 spin-system; methyl NMR; methyl axis order parameters; proteins; side-chain dynamics.