The alpha 1a and alpha 1b-adrenergic receptor subtypes: molecular mechanisms of receptor activation and of drug action

The Camerino symposium series (1978-2013): a privileged observatory of receptorology development

The organizers of the Camerino Receptor Symposia survey the development of receptorology. They trace the course from the first Symposium in 1978, which laid the foundation for Pirenzepine, the first selective muscarinic antagonist, to the 2010 Symposium, which highlighted the utility of functional simple domain antibodies (nanobodies) as novel G Protein-Coupled Receptor (GPCR) modulators. This 30-year period sees the acceptance of terms such as G-protein, auto- and heteroreceptors, site-directed mutagenesis, chimeric receptors, constitutive activity, inverse agonism, and orphan receptors. GPCRs are finally a reality and Langley and Ehrlich, if they returned to their laboratories, would be proud of how their intuitions have been realized.

Two model system of the alpha1A-adrenoceptor docked with selected ligands

In this study, we have developed a two model system to mimic the active and inactive states of a G-protein coupled receptor specifically the alpha1A adrenergic receptor. We have docked two agonists, epinephrine (phenylamine type) and oxymetazoline (imidazoline type), as well as two antagonists, prazosin and 5-methylurapidil, into two alpha1A receptor models, active and inactive. The best docking complexes for both agonists had hydrophilic interactions with D106, while neither antagonist did. Prazosin and oxymetazoline had hydrophobic interactions with F308 and F312. We predict from our study that the active state is stabilized by the interaction of F193 with I114, L197, V278, F281, and V282. The active state is further stabilized by the interaction of F312 with L75, V79, and L80. We also predict that the inactive state of the receptor is stabilized by the interaction of F312 with W102, F288, and M292.

Computational development of an α1A-adrenoceptor model in a membrane mimic

A number of subtypes of the alpha-adrenoceptor have been identified; however, knowledge of the three-dimensional structures of such membrane proteins is limited, and no crystal structure of an alpha-adrenoceptor is available to date. We have developed and analysed homology models of the alpha1A-adrenoceptor subtype based on the bovine rhodopsin crystal structure (1l9 h). Subsequent structural refinement was performed through molecular dynamics simulations using the Amber 7 suite of programs with a biphasic H2O/CHCl3/H2O cell utilised to mimic the receptor's natural membrane environment.

Structure–activity relationship of coordinated catecholamine in the [RuIII(NH3)4(catecholamine)]+ complex

The redox chemistry and pharmacological studies of the novel blue ruthenium(III)-catecholamine complexes were investigated in aqueous medium and compared to the free catecholamines. The [Ru(III)(NH3)4(catecholamine)]+ can be oxidized or reduced reversibly in one electron redox couples in aqueous solution. This is in contrast to the free catecholamines, which has a complicated electrochemical behavior due to coupled protonation process. The introduction of the ruthenium group reduces the intrinsic efficacy of the studied catecholamines. The [Ru(III)(NH3)4(catecholamine)]+ complex aqueous medium is more stable than the free catecholamines ligand in the same conditions.

Sequence analysis reveals how G protein-coupled receptors transduce the signal to the G protein

Sequence entropy-variability plots based on alignments of very large numbers of sequences-can indicate the location in proteins of the main active site and modulator sites. In the previous article in this issue, we applied this observation to a series of well-studied proteins and concluded that it was possible to detect most of the residues with a known functional role. Here, we apply the method to rhodopsin-like G protein-coupled receptors. Our conclusion is that G protein binding is the main evolutionary constraint on these receptors, and that other ligands, such as agonists, act as modulators. The activation of the receptors can be described as a simple, two-step process, and the residues involved in signal transduction can be identified.

Structure modeling of the chemokine receptor CCR5: implications for ligand binding and selectivity

The G-protein coupled receptor CCR5 is the main co-receptor for macrophage-tropic HIV-1 strains. I have built a structural model of the chemokine receptor CCR5 and used it to explain the binding and selectivity of the antagonist TAK779. Models of the extracellular (EC) domains of CCR5 have been constructed and used to rationalize current biological data on the binding of HIV-1 and chemokines. Residues spanning the transmembrane region of CCR5 have been modeled after rhodopsin, and their functional significance examined using the evolutionary trace method. The receptor cavity shares six residues with CC-chemokine receptors CCR1 through CCR4, while seven residues are unique to CCR5. The contribution of these residues to ligand binding and selectivity is tested by molecular docking simulations of TAK779 to CCR1, CCR2, and CCR5. TAK779 binds to CCR5 in the cavity formed by helices 1, 2, 3, and 7 with additional interactions with helices 5 and 6. TAK779 did not dock to either CCR1 or CCR2. The results are consistent with current site-directed mutagenesis data and with the observed selectivity of TAK779 for CCR5 over CCR1 and CCR2. The specific residues responsible for the observed selectivity are identified. The four EC regions of CCR5 have been modeled using constrained simulated annealing simulations. Applied dihedral angle constraints are representative of the secondary structure propensities of these regions. Tertiary interactions, in the form of distance constraints, are generated from available epitope mapping data. Analysis of the 250 simulated structures provides new insights to the design of experiments aimed at determining residue-residue contacts across the EC domains and for mapping CC-chemokines on the surface of the EC domains.