Structural implications of a Val -> Glu mutation in transmembrane peptidesfrom the EGF receptor

Certain specific point mutations within the transmembrane domains of class I receptor tyrosine kinases are known to induce altered behavior in the hos t cell. An internally controlled pair of peptides containing the transmembr ane portion of the human epidermal growth factor (EGF) receptor (ErbB-1) wa s examined in fluid, fully hydrated lipid bilayers by wide-line H-2-NMR for insight into the physical basis of this effect. One member of the pair enc ompassed the native transmembrane sequence from ErbB-1, while in the other the valine residue at position 627 was replaced by glutamic acid to mimic a substitution that produces a transformed phenotype in cells. Heteronuclear probes having a defined relationship to the peptide backbone were incorpor ated by deuteration of the methyl side chains of natural alanine residues. H-2-NMR spectra were recorded in the range 35 degreesC to 65 degreesC in me mbranes composed of 1-palmitoyl-2-oleoyl phosphatidylcholine. Narrowed spec tral components arising from species rotating rapidly and symmetrically wit hin the membrane persisted to very high temperature and appeared to represe nt monomeric peptide. Probes at positions 623 and 629 within the EGF recept or displayed changes in quadrupole splitting when Val(627) was replaced by Glu, while probes downstream at position 637 were relatively unaffected. Th e results demonstrate a measurable spatial reorientation in the region of t he 5-amino acid motif (residues 624-628) often suggested to be involved in side-to-side interactions of the receptor transmembrane domain. Spectral ch anges induced by the Val --> Glu mutation in ErbB-1 were smaller than those induced by the analogous oncogenic mutation in the homologous human recept or, ErbB-2 (Sharpe, S., K. R. Barber, and C. W. M. Grant. 2000. Biochemistr y. 39:6572-6580). Quadrupole splittings at probe sites examined were only m odestly sensitive to temperature, suggesting that each transmembrane peptid e behaved as a motionally ordered unit possessing considerable conformation al stability.