Multiple Activation Steps of the N -Formyl Peptide Receptor † (original) (raw)
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Lessons from constitutively active mutants of G protein-coupled receptors
Trends in Endocrinology & Metabolism, 2002
In the past decade, the concept of constitutive activity has profoundly modified our understanding of G protein-coupled-receptors (GPCRs). Here, we review the contribution of constitutively active mutants (CAMs) to our understanding of three aspects of GPCR physiopathology: (1) GPCR activation is a complex mechanism involving both the release of inactive state conformational constraints, mimicked by most CAMs, and the creation of new interactions that stabilize the active state and are mimicked by a restricted set of CAMs; (2) GPCR phosphorylation, internalization and desensitization processes are activated by receptor conformations, which partly overlap those activating G protein; (3) natural CAMs, mostly affecting GPCRs of the endocrine system, are found in several hereditary and acquired diseases, including cancers. One major remaining question is how CAMs recapitulate the different structural modifications of the agonist-induced active conformation(s) of the wild-type receptor. This characterization is a prerequisite for further use of CAMs as ligand-free models of active GPCRs in structural, cellular and physiological studies.
Pharmacology & Therapeutics, 2004
The superfamily of G-protein-coupled receptors (GPCRs) could be subclassified into 7 families (A, B, large N-terminal family B-7 transmembrane helix, C, Frizzled/Smoothened, taste 2, and vomeronasal 1 receptors) among mammalian species. Cloning and functional studies of GPCRs have revealed that the superfamily of GPCRs comprises receptors for chemically diverse native ligands including (1) endogenous compounds like amines, peptides, and Wnt proteins (i.e., secreted proteins activating Frizzled receptors); (2) endogenous cell surface adhesion molecules; and (3) photons and exogenous compounds like odorants. The combined use of site-directed mutagenesis and molecular modeling approaches have provided detailed insight into molecular mechanisms of ligand binding, receptor folding, receptor activation, G-protein coupling, and regulation of GPCRs. The vast majority of family A, B, C, vomeronasal 1, and taste 2 receptors are able to transduce signals into cells through G-protein coupling. However, G-protein-independent signaling mechanisms have also been reported for many GPCRs. Specific interaction motifs in the intracellular parts of these receptors allow them to interact with scaffold proteins. Protein engineering techniques have provided information on molecular mechanisms of GPCR-accessory protein, GPCR-GPCR, and GPCR-scaffold protein interactions. Site-directed mutagenesis and molecular dynamics simulations have revealed that the inactive state conformations are stabilized by specific interhelical and intrahelical salt bridge interactions and hydrophobic-type interactions. Constitutively activating mutations or agonist binding disrupts such constraining interactions leading to receptor conformations that associates with and activate G-proteins. .no (K. Kristiansen).
cDNA cloning of a novel G protein-coupled receptor with a large extracellular loop structure
Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression, 1996
A cDNA designated as AZ3B has been isolated from a differentiated HL-60 cell cDNA library with a probe derived from the N-formyl peptide receptor gene. The 1.97-kb cDNA encodes a novel G protein-coupled receptor (GPCR) with 482 amino acids. In addition to the predicted 7 transmembrane domains common to all GPCRs, the protein encoded by AZ3B contains a large extracellular loop of ~ 172 amino acids between the fourth and the fifth transmembrane domains, a feature unique among the hundreds of GPCRs identified to date. High sequence homology exists between the AZ3B protein and a number of chemoattractant receptors in the amino-terminal 170 residues and the carboxyl-terminal 150 residues. Northern and flow cytometric analyses suggested that the AZ3B message and protein are widely expressed in several differentiated hematopoietic cell lines, in the lung, placenta, heart, and endothelial cells. We postulate that the AZ3B protein defines a distinct group of receptors within the GPCR superfamily.
Receptor-Mediated Activation of Heterotrimeric G-Proteins: Current Structural Insights
Molecular Pharmacology, 2007
G-protein-coupled receptors (GPCRs) serve as catalytic activators of heterotrimeric G-proteins (G␣␥) by exchanging GTP for the bound GDP on the G␣ subunit. This guanine nucleotide exchange factor activity of GPCRs is the initial step in the G-protein cycle and determines the onset of various intracellular signaling pathways that govern critical physiological responses to extracellular cues. Although the structural basis for many steps in the G-protein nucleotide cycle have been made clear over the past decade, the precise mechanism for receptor-mediated Gprotein activation remains incompletely defined. Given that these receptors have historically represented a set of rich drug targets, a more complete understanding of their mechanism of action should provide further avenues for drug discovery. Several models have been proposed to explain the communication between activated GPCRs and G␣␥ leading to the structural changes required for guanine nucleotide exchange. This review is focused on the structural biology of G-protein signal transduction with an emphasis on the current hypotheses regarding G␣␥ activation. We highlight several recent results shedding new light on the structural changes in G␣ that may underlie GDP release. Many key extracellular signals, including hormones, neurotransmitters, growth factors, and sensory stimuli, relay information intracellularly by activation of plasma membrane-bound receptors. The largest class of such receptors is the superfamily of heptahelical G-protein-coupled receptors (GPCRs). In many genomes, GPCRs are encoded by the largest gene family; in humans, Ͼ1% of the genome is dedicated to producing hundreds of these critical signal detectors (Takeda et al., 2002; Fredriksson et al., 2003). Genetic studies have highlighted the physiological importance of GPCRs, with knockout models revealing pathological phenotypes involving the cardiovascular, nervous, endocrine, and sensory systems (Rohrer and Kobilka, 1998; Yang et al., 2002; Karasinska et al., 2003). Several hereditary diseases have also been linked to mutations within the genes encoding specific GPCRs (Spiegel and Weinstein, 2004). Indeed, GPCRs represent a major therapeutic target, giving rise to the largest single fraction of the prescription drug market, with annual sales of several billion dollars (Overington et al., 2006). Therefore, a complete mechanistic understanding of how GPCRs communicate extracellular signals into the cell would be extremely valuable for the continued development of novel therapeutics that target this family of receptors and the signaling cascades they modulate. G-Protein Signaling and the Guanine Nucleotide Cycle GPCRs transduce signals by activating heterotrimeric Gproteins that normally exist in an inactive state of G␣-GDP bound to G␥ subunits (Fig. 1). Agonist activation of GPCRs induces a conformational change within the receptor, which subsequently catalyzes the exchange of GDP for GTP on the G␣ subunit (Gilman, 1987). In this way, GPCRs serve as guanine nucleotide exchange factors (GEFs) for G␣-GDP/G␥ complexes (Fig. 1). Although the exact mechanism by which GPCRs exert their GEF activity remains to be fully eluci-The writing of this review was made possible by generous funding support (F32-GM076944, R01-GM062338, and R01-GM074268) from the National Institute of General Medical Sciences. Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
The Journal of biological chemistry, 2003
The histamine H1 receptor and the ␣ 1b -adrenoreceptor are G protein-coupled receptors that elevate intracellular [Ca 2؉ ] via activation of G q /G 11 . Assessed by coimmunoprecipitation and time-resolved fluorescence resonance energy transfer they both exist as homodimers. The addition of the G protein G 11 ␣ to the C terminus of these receptors did not prevent dimerization. Agonists produced a large stimulation of guanosine