Although homo- and heterodimerizations of G protein-coupled receptors (GPCRs) are well documented, GPCR monomers are able to assemble in different ways, thus causing variations in the interactive interface between receptor monomers among different GPCRs. Moreover, the functional consequences of this phenomenon, which remain to be clarified, could be specific for different GPCRs. Synthetic peptides derived from transmembrane (TM) domains can interact with a full-length GPCR, blocking dimer formation and affecting its function. Here we used peptides corresponding to TM helices of bovine rhodopsin (Rho) to investigate the Rho dimer interface and functional consequences of its disruption. Incubation of Rho with TM1, TM2, TM4, and TM5 peptides in rod outer segment (ROS) membranes shifted the resulting detergent-solubilized protein migration through a gel filtration column toward smaller molecular masses with a reduced propensity for dimer formation in a cross-linking reaction. Binding of these TM peptides to Rho was characterized by both mass spectrometry and a label-free assay from which dissociation constants were calculated. A BRET (bioluminescence resonance energy transfer) assay revealed that the physical interaction between Rho molecules expressed in membranes of living cells was blocked by the same four TM peptides identified in our in vitro experiments. Although disruption of the Rho dimer/oligomer had no effect on the rates of G protein activation, binding of G_t to the activated receptor stabilized the dimer. However, TM peptide-induced disruption of dimer/oligomer decreased receptor stability, suggesting that Rho supramolecular organization could be essential for ROS stabilization and receptor trafficking.

The rise of SARS-CoV-2 variants, with changes that could be related to an increased virus pathogenicity, have received the interest of the scientific and medical community. In this study, we evaluated the changes that occurred in the viral spike of the SARS-CoV-2 Omicron variant and whether these changes modulate the interactions with the angiotensin-converting enzyme 2 (ACE2) host receptor. The mutations associated with the Omicron variant were retrieved from the GISAID and covariants.org databases, and a structural model was built using the SWISS-Model server. The interaction between the spike and the human ACE2 was evaluated using two different docking software, Zdock and Haddock. We found that the binding free energy was lower for the Omicron variant as compared to the WT spike. In addition, the Omicron spike protein showed an increased number of electrostatic interactions with ACE2 than the WT spike, especially the interactions related to charged residues. This study contributes to a better understanding of the changes in the interaction between the Omicron spike and the human host ACE2 receptor.

A large body of evidence for G‐proteincoupled 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 (G _t ) 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 G _t . We found that only 50% of Rho* in the Rho*‐G _t 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 G _t 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.—Jastrzebska, B., Orban, T., Golczak, M., Engel, A., Palczewski, K. Asymmetry of the rhodopsin dimer in complex with transducin. FASEB J. 27, 1572–1584 (2013). www.fasebj.org