A Positively Charged Liquid Crystalline Medium for Measuring Residual Dipolar Couplings in Membrane Proteins by NMR

Residual Dipolar Couplings (RDCs) are integral to the refinement of membrane protein structures by NMR since they accurately define the orientation of helices and other structural units. Only a small set of liquid crystals used for RDC measurements are compatible with the detergents needed in membrane protein studies. The available detergent-compatible liquid crystals are negatively charged, thus offering effectively only one of five orthogonal components of the alignment Saupe matrix. In this communication, we present a robust liquid crystalline medium that is positively charged, pinacyanol acetate (PNA), for the determination of orthogonal sets of RDCs in membrane proteins. This new medium promises to enhance the accuracy of membrane protein structures and the measurement of dynamics based on RDCs.