Comparison of Solid-State Dipolar Couplings and Solution Relaxation Data Provides Insight into Protein Backbone Dynamics

Analyses of solution N-15 relaxation data and solid-state H-1(N)-N-15 dipolar couplings from a small globular protein, alpha-spectrin SH3 domain, produce a surprisingly similar pattern of order parameters. This result suggests that there is little or no ns-mu s dynamics throughout most of the sequence and, in particular, in the structured portion of the backbone. At the same time, evidence of ns-mu s motions is found in the flexible loops and termini. These findings, corroborated by the MD simulations of alpha-spectrin SH3 in a hydrated crystalline environment and in solution, are consistent with the picture of protein dynamics that has recently emerged from the solution studies employing residual dipolar couplings.