NMR Studies in Dodecylphosphocholine of a Fragment Containing the Seventh Transmembrane Helix of a G-Protein-Coupled Receptor from Saccharomyces cerevisiae

The structure and dynamics of a large segment of Ste2p, the G-protein-coupled α-factor receptor from yeast, were studied in dodecylphosphocholine (DPC) micelles using solution NMR spectroscopy. We investigated the 73-residue peptide EL3-TM7-CT40 consisting of the third extracellular loop 3 (EL3), the seventh transmembrane helix (TM7), and 40 residues from the cytosolic C-terminal domain (CT40). The structure reveals the presence of an α-helix in the segment encompassing residues 10–30, which is perturbed around the internal Pro-24 residue. Root mean-square deviation values of individually superimposed helical segments 10–20 and 25–30 were 0.91 ± 0.33 Å and 0.76 ± 0.37 Å, respectively. 15N-relaxation and residual dipolar coupling data support a rather stable fold for the TM7 part of EL3-TM7-CT40, whereas the EL3 and CT40 segments are more flexible. Spin-label data indicate that the TM7 helix integrates into DPC micelles but is flexible around the internal Pro-24 site, exposing residues 22–26 to solution and reveal a second site of interaction with the micelle within a region comprising residues 43–58, which forms part of a less well-defined nascent helix. These findings are discussed in light of previous studies in organic-aqueous solvent systems.