title: Asymmetry of the rhodopsin dimer in complex with transducin.
abstract: A large body of evidence for G-protein-coupled receptor (GPCR) oligomerization has accumulated over the past 2 decades. The smallest of these oligomers in vivo most likely is a dimer that buries 1000-Å(2) intramolecular surfaces and on stimulation forms a complex with heterotrimeric G protein in 2:1 stoichiometry. However, it is unclear whether each of the monomers adopts the same or a different conformation and function after activation of this dimer. With bovine rhodopsin (Rho) and its cognate bovine G-protein transducin (Gt) as a model system, we used the retinoid chromophores 11-cis-retinal and 9-cis-retinal to monitor each monomer of the dimeric GPCR within a stable complex with nucleotide-free Gt. We found that only 50% of Rho* in the Rho*-Gt complex is trapped in a Meta II conformation, while 50% evolves toward an opsin conformation and can be regenerated with 9-cis-retinal. We also found that all-trans-retinal can regenerate chromophore-depleted Rho*e complexed with Gt and FAK*TSA peptide containing Lys(296) with the attached all-trans retinoid (m/z of 934.5[MH](+)) was identified by mass spectrometry. Thus, our study shows that each of the monomers contributes unequally to the pentameric (2:1:1:1) complex of Rho dimer and Gt heterotrimer, validating the oligomeric structure of the complex and the asymmetry of the GPCR dimer, and revealing its structural/functional signature. This study provides a clear functional distinction between monomers of family A GPCRs in their oligomeric form.
authors.affiliation: Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA.
authors.forename: Beata
authors.initials: B
authors.lastname: Jastrzebska
authors.forename: Tivadar
authors.initials: T
authors.lastname: Orban
authors.forename: Marcin
authors.initials: M
authors.lastname: Golczak
authors.forename: Andreas
authors.initials: A
authors.lastname: Engel
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Palczewski
mesh_terms: D001665:Binding Sites / Q000502:physiology; D004224:Diterpenes; D008958:Models, Molecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012172:Retinaldehyde / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D015293:Transducin / Q000737:chemistry* / Q000378:metabolism
chemical_list: D004224:Diterpenes; C031390:9-cis-retinal; D012243:Rhodopsin; D015293:Transducin; D012172:Retinaldehyde