Arrangement of rhodopsin transmembrane α-helices

Abstract

Rhodopsins, the photoreceptors in rod cells, are G-protein-coupled receptors with seven hydrophobic segments containing characteristic conserved sequence patterns that define a large family. Members of the family are expected to share a conserved transmembrane structure. Direct evidence for the arrangement of seven alpha-helices was obtained from a 9A projection map of bovine rhodopsin. Structural constraints inferred from a comparison of G-protein-coupled receptor sequences were used to assign the seven hydrophobic stretches in the sequence to features in the projection map. A low-resolution three-dimensional structure of bovine rhodopsin and two projection structures of frog rhodopsin confirmed the position of the three least tilted helices, 4, 6 and 7. A more elongated peak of density for helix 5 indicated that it is tilted or bent, but helices 1, 2 and 3 were not resolved. Here we have used electron micrographs of frozen-hydrated two-dimensional frog rhodopsin crystals to determine the structure of frog rhodopsin. Seven rods of density in the map are used to estimate tilt angles for the seven helices. Density visible on the extracellular side of the membrane suggests a folded domain. Density extends from helix 6 on the intracellular side, and a short connection between helices 1 and 2, and possibly a part of the carboxy terminus, are visible.

Identification of Two Pairs of Spatially Approximated Residues within the Carboxyl Terminus of Secretin and Its Receptor

“…Unfortunately, our understanding of the conformation of receptors in the class II family of G protein-coupled receptors is quite limited, being largely confined to the theoretical prediction of the confluence of helices (25,26). These predictions have been based on existing helical bundle models of class I G protein-coupled receptors (27)(28)(29), with refinement based on sequence homologies between class I and II receptors, as well as the chemical character of residues that are conserved and divergent among the members of the class II family. The amino-terminal tail and extracellular loop regions that have been shown to be relevant to natural ligand binding for these receptors have been absent from such models.…”

1 H and 13 C MAS NMR evidence for pronounced ligand–protein interactions involving the ionone ring of the retinylidene chromophore in rhodopsin

“…The GPCRs play an essential role in the transduction of signals from the extracellular environment across the plasma membrane to the interior of every cell type and thus represent an important target for pharmacological intervention (1). Rhodopsin consists of 348-aa residues arranged in seven transmembrane ␣-helices that span the disk membranes of the rod outer segment (2)(3)(4). The chromophore of rhodopsin is an 11-cisretinylidene prosthetic group that is bound to the protein via a protonated Schiff base (pSB) linkage to amino acid residue Lys-296 (Fig.…”

The rat adenine receptor: pharmacological characterization and mutagenesis studies to investigate its putative ligand binding site

“…The protein bands were detected at 35 kDa. Additional rAdeR-specific bands were detected between about 60 and 70 kDa possibly representing receptor dimers ab initio and assembled using coordinates from the frog rhodopsin 2D X-ray projection structure [35,36]. Heo et al suggested Phe110 3.24 , Asn115 3.29 , Asn173 4.60 , Leu201 5.47 , and His252 6.54 to be involved in adenine binding.…”

“…Four injections were performed before serum collection. To gain better specificity, additional antibodies were raised against the following peptides: [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] (N-term), 181-194 (extracellular loop 2 (ECL2)), 222-235 (intracellular loop 3 (ICL3)), 295-314 (C-terminal), and 313-331 (C-terminal). These antibodies were produced in two rabbits each by Thermo Scientific.…”