Use of nuclear magnetic resonance to study the three-dimensional structure of rhodopsin

G protein-coupled receptors are believed to be built around a bundle of seven transmembrane helices. This chapter presents a model that suggests that much of the secondary structure of these proteins is contained in the transmembrane helices and the turns that connect them. It can be hypothesized that information about secondary structure—such as helices and turns—can be obtained from peptides designed to contain the sequences from the protein that putatively code for these secondary structures. Nuclear magnetic resonance (NMR) structural studies of small peptides spanning about three-fourths (both helices and loops) of the soluble four-helix bundle, myohemerythrin, showed the same secondary structure in solution as those sequences adopt in the intact protein. None of the peptides showed a structure in solution that was different from the native protein. In proteins consisting of helical bundles, much of the secondary structure of the native protein is retained in small peptides spanning the sequence of the helical bundle.