Protein structure in anisotropic environments: Development of orientational constraints

Solid state nuclear magnetic resonance has the potential to characterize membrane protein structures at very high resolution. This paper focuses on the use of orientational constraints for this purpose. These constraints are based on observing the orientation dependence of nuclear spin interactions. The interpretation of these observations is based on accurate knowledge of the spin interaction tensors—the tensor element magnitudes and their orientation to the molecular frame. Numerous possibilities exist for developing these orientational constraints, each with their own strengths and weaknesses. This first of two papers focuses on the observation of these constraints and their inherent error, while the second paper demonstrates the utility, advantages, and disadvantages of these constraints for solving protein backbone structure.