SEQUENCE AND STRUCTURE OF THE MEMBRANE-ASSOCIATED PEPTIDE OF GLYCOPHORIN-A

Glycophorin A (GPA) has been reconstituted into dimyristoylphosphatidy lcholine vesicles and digested with proteinase K to identify the membr ane domain and to characterize its structure and orientation. After di gestion of the inner and outer domain of GPA by protease action restri cted to the aqueous phase, a protected peptide migrates on an electrop horesis gel as a 7.5-kDa dimer (His(66)-Ile(95)). The secondary struct ure and orientation in a lipid bilayer of the 7.5-kDa dimer have been studied by Fourier transform infrared spectroscopy. Our proteolytic an d spectroscopic data are in agreement with a topological model in whic h the His(66)-Glu(72) peptide adopts a beta-sheet conformation and is oriented parallel to the lipid-water interface and the Ile(73)-Ile(95) domain is helical and oriented parallel to the lipid acyl chains, in a transmembrane configuration. Digestion of the domain protruding to t he outside of the liposome generates ''head-head'' and ''head-tail'' d imers of 16 and 38 kDa, respectively. This observation is discussed in terms of the specificity of the dimer formation process.