ABSTRACT
Most studies suggest that the transmembrane segments have appreciable a helical structures with helices oriented perpendicular to the membrane surface. Although the extramembranous portion of several other membrane-associated proteins have been solved to high resolution, structural information for proteins which have a large fraction of their mass intimately associated with the lipid bilayer is at too low a level of resolution to identify individual amino acids. Resonance energy transfer (RET), in contrast, is well-understood and can, therefore, be used to localize membrane protein regions to high resolution. RET methods applied to the study of membrane protein structure are generally of two types. In the first, the protein is labeled with covalent probes and therefore transfer is measured between discrete donor-acceptor pairs. In the second, RET is measured between an intrinsic donor or acceptor and a complementary chromophore which forms a noncovalent association with the membrane, usually a lipid probe.
