Assessment of protein alignment using 1H-1H residual dipolar coupling measurements

A quick and accurate method is described for assessing protein alignment from residual dipolar coupling (RDC) measurements. In contrast to observing D2O resonance splitting, which reflects the orientational order of the alignment medium, the degree of alignment of a protein of interest can be estimated directly from 1H-1H RDCs. In this study, RDCs between aromatic protons in unlabeled Cp-rubredoxin were measured from proton homonuclear J-resolved experiments with high sensitivity, and the alignment was assessed without the need of extensive resonance assignment. Since labeled proteins are not needed, this method provides an efficient way for screening alignment media. In situations where the protein structure is known, as in the case of Cp-rubredoxin, a full set of order tensor parameters can be determined, allowing further studies, such as those of ligand alignment relative to a target protein.