Comparative Study of REDOR and CPPI Derived Order Parameters by 1H-Detected MAS NMR and MD Simulations

5 years ago

Comparative Study of REDOR and CPPI Derived Order Parameters by 1H-Detected MAS NMR and MD Simulations

Bernd Reif, Sam Asami

The measurement of dipolar couplings among directly bonded nuclei yields direct information on the amplitude of dynamic processes in the solid-state. For a reliable motional analysis using, e.g., the model-free approach, a correct quantification of the absolute values of these order parameters is absolutely essential. In the absence of a reference value for the rigid limit, too low dipolar coupling values might be misinterpreted as motion. Therefore, a detailed understanding of the effects that influence the quantification of the experimental order parameters is necessary. We compare here REDOR and CPPI derived order parameters assessed in ¹H-detected experiments, and discuss the influence of remote protons and rf inhomogeneity on the extracted dipolar coupling constant for MAS rotation frequencies in the range 20–100 kHz. Experimental results are furthermore compared with the order parameter obtained from a molecular dynamics simulation. We find that fast magic-angle spinning up to 100 kHz can yield artifact-free REDOR based ¹H,¹⁵N order parameters for perdeuterated and 100% amide back-exchanged proteins, and potentially even in uniformly protonated samples. We believe that awareness of systematic errors introduced by the measurement and in the analysis of order parameters will yield a better understanding of the dynamic properties of a protein derived from solid-state NMR observables.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcb.7b06812

DOI: 10.1021/acs.jpcb.7b06812