The Effects of Mutations on Motions of Side-chains in Protein L Studied by 2H NMR Dynamics and Scalar Couplings

Recently developed 2H spin relaxation experiments are applied to study the dynamics of methyl-containing side-chains in the B1 domain of protein L and in a pair of point mutants of the domain, F22L and A20V. X-ray and NMR studies of the three variants of protein L studied here establish that their structures are very similar, despite the fact that the F22L mutant is 3.2 kcal/mol less stable. Measurements of methyl 2H spin relaxation rates, which probe dynamics on a picosecond–nanosecond time scale, and three-bond 3JCγ–CO, 3JCγ–N and 3JCα–Cδ scalar coupling constants, which are sensitive to motion spanning a wide range of time-scales, reveal changes in the magnitude of side-chain dynamics in response to mutation. Observed differences in the time-scale of motions between the variants have been related to changes in energetic barriers. Of interest, several of the residues with different motional properties across the variants are far from the site of mutation, suggesting the presence of long-range interactions within the protein that can be probed through studies of dynamics.