[14] Nuclear magnetic resonance of membrane-associated peptides and proteins

Structural biology is based on the premise that the fundamental understanding of biological functions lies in the three-dimensional structures of proteins and other biopolymers. The two well-established experimental methods for determining the structures of proteins work very well for globular proteins: X-ray crystallography and nuclear magnetic resonance (NMR). However, approximately 30% of all expressed polypeptides are membrane-associated and neither X-ray crystallography nor solution NMR spectroscopy is very effective for these proteins. The development of bacterial expression systems is as important as that of pulse sequences or instrumentation for the success of NMR studies of membrane proteins. The ability to express membrane proteins in bacteria provides the opportunity to incorporate a variety of isotopic labeling schemes into the overall experimental strategy, because it allows both selective and uniform labeling. NMR spectroscopy can determine the structures of helical membrane proteins in micelles and bilayers. The initial results on functional peptides are being extended to proteins of some complexity, including those with more than one biological activity. The methods for expression and purification of these proteins from bacteria and the preparation of samples in lipids are as important as the instrumentation and methods for the NMR experiments.