Characterization of the proto-oncogenic and mutant forms of the transmembrane region of Neu in micelles.

ABSTRACT

We have investigated peptides corresponding to the complete transmembrane region of both proto-oncogenic (Val(664)) and mutant (Glu(664)) forms of the receptor Neu in detergent micelles by NMR and CD spectroscopy. Both forms of the peptide appear to adopt similar levels of helicity and dimeric interactions based on the analysis of CD spectra and nuclear Overhauser effect connectivity profiles. There are considerable differences in the chemical shifts of amide and, to a lesser extent, CHalpha resonances between the two forms of the peptides, and these differences are most pronounced in residues upstream of the mutation site and close to the N terminus of the transmembrane domain. Similarly, there are substantial differences in the amide hydrogen-deuterium exchange rates for residues close to and upstream of the mutation site; amide protons in this region of the protooncogenic peptide are much more resistant to exchange than those in the mutant form. In both molecules, residues downstream of the mutation site exhibit slow exchange. We therefore demonstrate that, although transmembrane Neu peptides exhibit similar levels of secondary structure when dispersed in detergent, there are detectable differences in their adopted micellar states that may provide insight into the dimer-promoting ability of the polar transforming mutation.