Search

Most of our understanding of G protein-coupled receptor (GPCR) activation has been focused on the direct interaction between diffusible ligands and their seven-transmembrane domains. However, a number of these receptors depend on their extracellular N-terminal domain for ligand recognition and activation. To dissect the molecular interactions underlying both modes of activation at a single receptor, we used the unique properties of the melanocortin-4 receptor (MC4R), a GPCR that shows constitutive activity maintained by its N-terminal domain and is physiologically activated by the peptide α-melanocyte stimulating hormone (αMSH). We find that activation by the N-terminal domain and αMSH relies on different key residues in the transmembrane region. We also demonstrate that agouti-related protein, a physiological antagonist of MC4R, acts as an inverse agonist by inhibiting N terminus-mediated activation, leading to the speculation that a number of constitutively active orphan GPCRs could have physiological inverse agonists as sole regulators.

There are few places where one is so exposed and vulnerable as in the analytic room. This is so for the patient and for the analyst, especially because patient and analyst share an openness with one another, a shared unconscious Us, that extends beyond their separate or 'bounded' minds. Indeed, it is shocking to experience how much more open and vulnerable to the other we are than we'd like to believe. Different authors have developed our understanding of the inevitable shared/common unconscious produced between patient and analyst. However, clinical manifestations of the patient-analyst's unconscious Us is deficient in the literature. There is even less written on what may be gained when adopting an Us perspective. This paper is a beginning step toward both goals. [ABSTRACT FROM AUTHOR]

The melanocortin 4 receptor (MC4R) is a G protein-coupled receptor mainly expressed in the central nervous system of vertebrates. Activation of the MC4R leads to a decrease in food intake, whereas inactivating mutations are a genetic cause of obesity. The binding of agouti-related protein (AGRP) reduces not only agonist-stimulated cAMP production (competitive antagonist) but also the basal activity of the receptor, as an inverse agonist. Transgenic zebrafish overexpressing AGRP display increased food intake and linear growth, indicative of a physiological role for the melanocortin system in the control of the energy balance in fish. We report on the cloning, pharmacological characterization, tissue distribution, and detailed brain mapping of a sea bass (Dicentrarchus labrax) MC4R ortholog. Sea bass MC4R is profusely expressed within food intake-controlling pathways of the fish brain. However, the activity of the melanocortin system during progressive fasting does not depend on the hypothalamic/pituitary proopiomelanocortin (POMC) and MC4R expression, which suggests that sea bass MC4R is constitutively activated and regulated by AGRP binding. We demonstrate that AGRP acts as competitive antagonist and reduces MTII-induced cAMP production. AGRP also decreases the basal activity of the receptor as an inverse agonist. This observation suggests that MC4R is constitutively active and supports the evolutionary conservation of the AGRP/MC4R interactions. The inverse agonism, but not the competitive antagonism, depends on the presence of a phosphodiesterase inhibitor (IBMX). This suggests that inverse agonism and competitive antagonism operate through different intracellular signaling pathways, a view that opens up new targets for the treatment of melanocortin-induced metabolic syndrome. melanocyte-stimulating hormone; proopiomelanocortin; constitutive activity; 3-isobutyl-l-methylxanthine; obesity

Author(s): Mark B. Pepys (corresponding author) [1]; Gideon M. Hirschfield [1, 6]; Glenys A. Tennent [1]; J. Ruth Gallimore [1]; Melvyn C. Kahan [1]; Vittorio Bellotti [1, 6]; Philip N. [...]

Research has been conducted on human group IIA secreted phospholipase A (sub)2. The preparation of phospholipase's H48Q and H48N mutants and the analysis of H48N and H48Q enzymes' activity are discussed.

The designed mini agouti-related protein, containing a 34-residue and a cystine knot architecture, functions as an antagonist with the melanocortin receptor contact points. This new molecule is useful for probing structure and function of melanocortin receptor.

Nuclear paramagnetic resonance spectra of the agouti-related protein demonstrate that the first 16 amino acid residues of the fold motif of the C-terminal domain of the protein confer melanocortin receptors' selectivity.

Comparison of the structure of vMIP-II with eotaxin-1, RANTES and MCP-3 suggests a unique mechanism for CCR3 activation.

Stromal cell-derived factor-1[Alpha] (SDF-1[Alpha]) is a member of the chemokine superfamily and functions as a growth factor and chemoattractant through activation of CXCR4/LESTR/Fusin, a G protein.coupled receptor. This receptor also functions as a coreceptor for T-tropic syncytium-inducing strains of HIV-1. SDF-1[Alpha] antagonizes infectivity of these strains by competing with gp120 for binding to the receptor. The crystal structure of a variant SDF-1[Alpha] ([N33A]SDF-1[Alpha]) prepared by total chemical synthesis has been refined to 2.2-[Angstrom] resolution. Although SDF-1[Alpha] adopts a typical chemokine [Beta]-[Beta]-[Beta]-[Alpha] topology, the packing of the [Alpha]-helix against the [Beta]-sheet is strikingly different. Comparison of SDF-1[Alpha] with other chemokine structures confirms the hypothesis that SDF-1[Alpha] may be either an ancestral protein from which all other chemokines evolved or the chemokine that is the least divergent from a primordial chemokine. The structure of SDF-1[Alpha] reveals a positively charged surface ideal for binding to the negatively charged extracellular loops of the CXCR4 HIV-1 coreceptor. This ionic complementarity is likely to promote the interaction of the mobile N-terminal segment of SDF-1[Alpha] with interhelical sites of the receptor, resulting in a biological response.