The EGF receptor transmembrane domain: Peptide-peptide interactions in fluid bilayer membranes

A peptide containing the transmembrane domain of the human EGF receptor was studied in fluid lipid bilayers for insight into receptor tyrosine kinase lateral associations in cell membranes. The peptide comprised the 23-amino acid hydrophobic segment thought to span the membrane (Ile(622) to Met(644) Of the EGF receptor), plus the first 10 amino acids of the receptor's cyto plasmic domain (Arg(645) to Th-654). Probes for solid-state NMR spectroscop y were incorporated by deuteration of the methyl side chains of alanine at positions 623 and 637, H-2-NMR spectra were recorded from 25 to 65 degrees C in membranes composed of 1-palmitoyl-2-oleoyl phosphatidylcholine, with a nd without 33% cholesterol, and relaxation times were measured, Peptide con centration ranged from 0.5 to 10 mot %, The peptide behaved as predominant monomers undergoing rapid symmetric rotational diffusion; however, there wa s evidence of reversible side-to-side interaction among the hydrophobic tra nsmembrane domains, particularly at physiological temperatures and in the p resence of natural concentrations of cholesterol. The results of these expe riments in fluid membranes are consistent with the existence of lipid-prote in interactions that would predispose to receptor microdomain formation in membranes of higher animal cells.