Rapid Determination of Fast Protein Dynamics from NMR Chemical Exchange Saturation Transfer Data

Functional motions of N-15-labeled proteins can be monitored by solution NMR spin relaxation experiments over a broad range of timescales. These experiments however typically take of the order of several days to a week per protein. Recently, NMR chemical exchange saturation transfer (CEST) experiments have emerged to probe slow millisecond motions complementing R-1 and CPMG-type experiments. CEST also simultaneously reports on site-specific R-1 and R-2 parameters. It is shown here how CEST-derived R-1 and R-2 relaxation parameters can be measured within a few hours at an accuracy comparable to traditional relaxation experiments. Using a lean version of the model-free approach S-2 order parameters can be determined that match those from the standard model-free approach applied to N-15 R-1, R-2, and {H-1}-N-15 NOE data. The new methodology, which is demonstrated for ubiquitin and arginine kinase (42kDa), should serve as an effective screening tool of protein dynamics from picosecond-to-millisecond timescales.