Crystal structure of opsin in its G-protein-interacting conformation

Abstract

Opsin, the ligand-free form of the G-protein-coupled receptor rhodopsin, at low pH adopts a conformationally distinct, active G-protein-binding state known as Ops*. A synthetic peptide derived from the main binding site of the heterotrimeric G protein-the carboxy terminus of the alpha-subunit (GalphaCT)-stabilizes Ops*. Here we present the 3.2 A crystal structure of the bovine Ops*-GalphaCT peptide complex. GalphaCT binds to a site in opsin that is opened by an outward tilt of transmembrane helix (TM) 6, a pairing of TM5 and TM6, and a restructured TM7-helix 8 kink. Contacts along the inner surface of TM5 and TM6 induce an alpha-helical conformation in GalphaCT with a C-terminal reverse turn. Main-chain carbonyl groups in the reverse turn constitute the centre of a hydrogen-bonded network, which links the two receptor regions containing the conserved E(D)RY and NPxxY(x)(5,6)F motifs. On the basis of the Ops*-GalphaCT structure and known conformational changes in Galpha, we discuss signal transfer from the receptor to the G protein nucleotide-binding site.

The structure of active opsin as a basis for identification of GPCR agonists by dynamic homology modelling and virtual screening assays

“…While helix I to IV are in excellent agreement (RMSD about 1 Å), helices V to VII deviate up to 3.0 Å from their position in the active state crystal structure. The outward movement of the intracellular side of helix VI, defined by the opsin structure, is less pronounced in the model than in the active B2AR crystal structures, indicating that the opsin structure might not resemble a fully activated GPCR state [15], or that the extend of this movement during activation is different between the two receptors.…”

Beyond spectral tuning: human cone visual pigments adopt different transient conformations for chromophore regeneration

“…Homology models for the dark state and active human red and green opsin were constructed, respectively, based on the crystal structure of bovine rhodopsin (PDB id: 1GZM) [ 22 ] and the opsin soaked with ATR (PDB id: 2X72) [ 23 ]. Modeller 9.8 was used for this purpose [ 24 ].…”

Position of Transmembrane Helix 6 Determines Receptor G Protein Coupling Specificity

“…However, the reverse turn of GsαCT is bulkier than those of GtαCT and its close homologue GiαCT ( Figure S9). Specifically, the cation−π interaction between Y391 and R131 3.50 in the β 2 AR*·Gs complex seems to require a 5−6 Å larger TM6 outward tilt than the hydrogen bond between the carbonyl oxygen of C347 and the guanidinium group of R135 3.50 in RhR*·GtαCT 6 ( Figure 1A,B). The present study was thus motivated by the idea that the different space requirements for the key interactions of GtαCT and GsαCT with R* result in distinct TM6 outward tilts and differently shaped cytoplasmic crevices in the corresponding complexes ( Figure 1C,D).…”

“…The starting position of GiαCT 19 was extrapolated from the crystal structure complex of GtαCT 19 ( 332 FDAVTDIIIKENLKDCGLF 350 ) with RhR*. 6 The receptor coordinates were taken from the β 2 AR*·Gs crystal structure complex. 7 In this starting configuration GiαCT 19 does not have any contact with TM6.…”