title: Evidence that helix 8 of rhodopsin acts as a membrane-dependent conformational switch.
abstract: The crystal structure of rhodopsin revealed a cytoplasmic helical segment (H8) extending from transmembrane (TM) helix seven to a pair of vicinal palmitoylated cysteine residues. We studied the structure of model peptides corresponding to H8 under a variety of conditions using steady-state fluorescence, fluorescence anisotropy, and circular dichroism spectroscopy. We find that H8 acts as a membrane-surface recognition domain, which adopts a helical structure only in the presence of membranes or membrane mimetics. The secondary structural properties of H8 further depend on membrane lipid composition with phosphatidylserine inducing helical structure. Fluorescence quenching experiments using brominated acyl chain phospholipids and vesicle leakage assays suggest that H8 lies within the membrane interfacial region where amino acid side chains can interact with phospholipid headgroups. We conclude that H8 in rhodopsin, in addition to its role in binding the G protein transducin, acts as a membrane-dependent conformational switch domain.
authors.affiliation: Laboratory of Molecular Biology and Biochemistry, Howard Hughes Medical Institute, The Rockefeller University, New York, New York 10021, USA.
authors.forename: A Gopala
authors.initials: AG
authors.lastname: Krishna
authors.forename: Santosh T
authors.initials: ST
authors.lastname: Menon
authors.forename: Tracy J
authors.initials: TJ
authors.lastname: Terry
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Sakmar
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D015195:Drug Design; D008081:Liposomes / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry; D008954:Models, Biological; D008958:Models, Molecular; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008081:Liposomes; D008563:Membrane Lipids; D010446:Peptide Fragments; D012243:Rhodopsin