Anchoring of tryptophan and tyrosine analogs at the hydrocarbon-polar boundary in model membrane vesicles: parallax analysis of fluorescence quenching induced by nitroxide-labeled phospholipids.

The role of Trp and Tyr residues in determining membrane protein structure is particularly interesting because indole and phenol structures combine hydrophobic and polar groups, and it is hard to predict the exact region of the membrane at which their energy would be at a minimum. To determine the depths intrinsically favored by these residues, the locations of membrane-associating Trp and Tyr analogs have been determined using a fluorescence quenching technique able to measure depth at high resolution. They are found to locate at the same depths as Trp and Tyr in membrane proteins, 14-15 A from the bilayer center, which implies an important role for these residues in aligning membrane proteins in precise relationship to the lipid bilayer.