Structure and topology of a peptide segment of the 6th transmembrane domain of the Saccharomyces cerevisae alpha-factor receptor in phospholipid bilayers

A detailed analysis of the structure of an 18-residue peptide AQSLLVPSIIFIL AYSLK [M6(252-269, C252A)] in 1,2-dimyristoyl-sn-glycero-phosphocholine bil ayers was carried out using solid state NMR and attenuated total reflection Fourier transform infrared spectroscopy. The peptide corresponds to a port ion of the 6th transmembrane domain of the a-factor receptor of Saccharomyc es cerevisiae. Ten homologs of M6(252-269, C252A) were synthesized in which individual residues were labeled with N-15. One- and two-dimensional solid state NMR experiments were used to determine the chemical shifts and H-1-N -15 dipolar coupling constants for the N-15-labeled peptides in oriented di myristoylphosphatidylcholine bilayers on stacked glass plates. These parame ters were used to calculate the structure and orientation of M6(252-269, C2 52A) in the bilayers. The results indicate that the carboxyl terminal resid ues (9-14) are alpha -helical and oriented with an angle of about 8 degrees with respect to the bilayer normal. Independently, an attenuated total ref lection Fourier transform infrared spectroscopy analysis on M6(252-269, C25 2A) in a 1,2-dimyristoyl-sn-glycero-phosphocholine bilayer concluded that t he helix tilt angle was about 12.5 degrees. The results on the structure of M6(252-269, C252A) in bilayers are in good agreement with the structure de termined in trifluoroethanol/water solutions (B. Arshava et al. Biopolymers , 1998, Vol. 46, pp. 343-357). The present study shows that solid state NMR spectroscopy can provide high resolution information on the structure of t ransmembrane domains of a G protein-coupled receptor. (C) 2001 John Wiley & Sons, Inc.