Structural implications of a Val-->Glu mutation in transmembrane peptides from 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 host cell. An internally controlled pair of peptides containing the transmembrane portion of the human epidermal growth factor (EGF) receptor (ErbB-1) was examined in fluid, fully hydrated lipid bilayers by wide-line 2H-NMR for insight into the physical basis of this effect. One member of the pair encompassed 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 incorporated by deuteration of the methyl side chains of natural alanine residues. 2H-NMR spectra were recorded in the range 35 degrees C to 65 degrees C in membranes composed of 1-palmitoyl-2-oleoyl phosphatidylcholine. Narrowed spectral components arising from species rotating rapidly and symmetrically within the membrane persisted to very high temperature and appeared to represent monomeric peptide. Probes at positions 623 and 629 within the EGF receptor displayed changes in quadrupole splitting when Val(627) was replaced by Glu, while probes downstream at position 637 were relatively unaffected. The results demonstrate a measurable spatial reorientation in the region of the 5-amino acid motif (residues 624-628) often suggested to be involved in side-to-side interactions of the receptor transmembrane domain. Spectral changes induced by the Val-->Glu mutation in ErbB-1 were smaller than those induced by the analogous oncogenic mutation in the homologous human receptor, ErbB-2 (Sharpe, S., K. R. Barber, and C. W. M. Grant. 2000. Biochemistry. 39:6572-6580). Quadrupole splittings at probe sites examined were only modestly sensitive to temperature, suggesting that each transmembrane peptide behaved as a motionally ordered unit possessing considerable conformational stability.