Charged gels as orienting media for measurement of residual dipolar couplings in soluble and integral membrane proteins

Measurement of residual dipolar couplings for membrane proteins will dramatically improve the quality of the structures obtainable by solution NMR spectroscopy. While there has been some success in achieving alignment of membrane-bound peptides, there has been very limited success in achieving alignment for functional membrane proteins. Herein, we demonstrate that charged polyacrylamide-based copolymers are suitable for obtaining weak alignment of membrane proteins reconstituted in detergent micelles. Varying the copolymer compositions, we prepared positively, zwitterionic, and negatively charged gels that are very stable at low concentration and can be used for obtaining weak alignment by compression in an NMR tube. Application of this method is demonstrated for the integral membrane protein OmpA in DPC micelles.