G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily related proteins that are cell surface receptors that detect molecules outside the cell and activate cellular responses. They are coupled with G proteins. They pass through the cell membrane seven times in the form of six loops of amino acid residues, which is why they are sometimes referred to as seven-transmembrane receptors. Ligands can bind either to the extracellular N-terminus and loops or to the binding site within transmembrane helices. They are all activated by agonists, although a spontaneous auto-activation of an empty receptor has also been observed.
In chemistry, dimerization is the process of joining two identical or similar molecular entities by bonds. The resulting bonds can be either strong or weak. Many symmetrical chemical species are described as dimers, even when the monomer is unknown or highly unstable.
An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the agonist, while an inverse agonist causes an action opposite to that of the agonist.
Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs). Opioid receptors are distributed widely in the brain, in the spinal cord, on peripheral neurons, and digestive tract.
In pharmacology, an inverse agonist is a drug that binds to the same receptor as an agonist but induces a pharmacological response opposite to that of the agonist.
Functional selectivity is the ligand-dependent selectivity for certain signal transduction pathways relative to a reference ligand at the same receptor. Functional selectivity can be present when a receptor has several possible signal transduction pathways. To which degree each pathway is activated thus depends on which ligand binds to the receptor. Functional selectivity, or biased signaling, is most extensively characterized at G protein coupled receptors (GPCRs). A number of biased agonists, such as those at muscarinic M2 receptors tested as analgesics or antiproliferative drugs, or those at opioid receptors that mediate pain, show potential at various receptor families to increase beneficial properties while reducing side effects. For example, pre-clinical studies with G protein biased agonists at the μ-opioid receptor show equivalent efficacy for treating pain with reduced risk for addictive potential and respiratory depression. Studies within the chemokine receptor system also suggest that GPCR biased agonism is physiologically relevant. For example, a beta-arrestin biased agonist of the chemokine receptor CXCR3 induced greater chemotaxis of T cells relative to a G protein biased agonist.
In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. The etymology stems from Latin ligare, which means 'to bind'. In protein-ligand binding, the ligand is usually a molecule which produces a signal by binding to a site on a target protein. The binding typically results in a change of conformational isomerism (conformation) of the target protein. In DNA-ligand binding studies, the ligand can be a small molecule, ion, or protein which binds to the DNA double helix. The relationship between ligand and binding partner is a function of charge, hydrophobicity, and molecular structure.
In biochemistry, an orphan receptor is a protein that has a similar structure to other identified receptors but whose endogenous ligand has not yet been identified. If a ligand for an orphan receptor is later discovered, the receptor is referred to as an "adopted orphan". Conversely, the term orphan ligand refers to a biological ligand whose cognate receptor has not yet been identified.
In the field of molecular modeling, docking is a method which predicts the preferred orientation of one molecule to a second when a ligand and a target are bound to each other to form a stable complex. Knowledge of the preferred orientation in turn may be used to predict the strength of association or binding affinity between two molecules using, for example, scoring functions.
P2Y receptors are a family of purinergic G protein-coupled receptors, stimulated by nucleotides such as adenosine triphosphate, adenosine diphosphate, uridine triphosphate, uridine diphosphate and UDP-glucose.To date, 8 P2Y receptors have been cloned in humans: P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13 and P2Y14.
The μ-opioid receptors (MOR) are a class of opioid receptors with a high affinity for enkephalins and beta-endorphin, but a low affinity for dynorphins. They are also referred to as μ(mu)-opioid peptide (MOP) receptors. The prototypical μ-opioid receptor agonist is morphine, the primary psychoactive alkaloid in opium and for which the receptor was named, with mu being the first letter of Morpheus, the compound's namesake in the original Greek. It is an inhibitory G-protein coupled receptor that activates the Gi alpha subunit, inhibiting adenylate cyclase activity, lowering cAMP levels.
The δ-opioid receptor, also known as delta opioid receptor or simply delta receptor, abbreviated DOR or DOP, is an inhibitory 7-transmembrane G-protein coupled receptor coupled to the G protein Gi/G0 and has enkephalins as its endogenous ligands. The regions of the brain where the δ-opioid receptor is largely expressed vary from species model to species model. In humans, the δ-opioid receptor is most heavily expressed in the basal ganglia and neocortical regions of the brain.
Dopamine receptor D2, also known as D2R, is a protein that, in humans, is encoded by the DRD2 gene. After work from Paul Greengard's lab had suggested that dopamine receptors were the site of action of antipsychotic drugs, several groups, including those of Solomon H. Snyder and Philip Seeman used a radiolabeled antipsychotic drug to identify what is now known as the dopamine D2 receptor. The dopamine D2 receptor is the main receptor for most antipsychotic drugs. The structure of DRD2 in complex with the atypical antipsychotic risperidone has been determined.
Hydroxycarboxylic acid receptor 3 (HCA3), also known as niacin receptor 2 (NIACR2) and GPR109B, is a protein which in humans is encoded by the HCAR3 gene. HCA3, like the other hydroxycarboxylic acid receptors HCA1 and HCA2, is a Gi/o-coupled G protein-coupled receptor (GPCR). The primary endogenous agonists of HCA3 are 3-hydroxyoctanoic acid and kynurenic acid. HCA3 is also a low-affinity biomolecular target for niacin (aka nicotinic acid).
Brian Kent Kobilka is an American physiologist and a recipient of the 2012 Nobel Prize in Chemistry with Robert Lefkowitz for discoveries that reveal the workings of G protein-coupled receptors. He is currently a professor in the department of Molecular and Cellular Physiology at Stanford University School of Medicine. He is also a co-founder of ConfometRx, a biotechnology company focusing on G protein-coupled receptors. He was named a member of the National Academy of Sciences in 2011.
Stuart C. Sealfon is an American neurologist who studies the mechanisms of both the therapeutic and adverse effects of drugs. He was an early adopter of the use of massively parallel qPCR and fluorescent in situ hybridization to characterize cell response state and his research accomplishments have included the identification of the primary structure of the gonadotropin-releasing hormone receptor, finding new signaling pathways activated by drugs for Parkinson's disease, elucidating the mechanism of action of hallucinogens and finding a new brain receptor complex implicated in schizophrenia as a novel target for antipsychotics.
Trevena, Inc. is a clinical stage biopharmaceutical company, headquartered in Chesterbrook, Pennsylvania, USA, and is involved in the discovery and development of G-protein coupled receptors (GPCR) biased ligands. Trevena was founded in 2007 with technology licensed from Duke University, which originated in the labs of company founders Robert Lefkowitz winner of the 2012 Nobel Prize in Chemistry and Howard Rockman. Trevena's approach to drug discovery is based on utilizing ligand bias, or functional selectivity, at GPCR targets to produce drugs with improved efficacy and reduced side effect profiles. Trevena was named one of the top 15 US startups of 2008 by Business Week.
Sadashiva "Sadu" Karnik is an Indian-born American molecular biologist who is a Professor in the Molecular Medicine Department of Cleveland Clinic Lerner College of Medicine at Case Western Reserve University. He is the Principal Investigator of the Sadashiva Karnik Laboratory, at the Lerner Research Institute of Cleveland Clinic.
Bryan L. Roth is the Michael Hooker Distinguished Professor of Protein Therapeutics and Translational Proteomics, UNC School of Medicine. He is recognized for his discoveries and inventions in the general areas of molecular pharmacology, GPCR structure, and function and synthetic neurobiology. He is a member of the American Academy of Arts and Sciences (AAAS) and the National Academy of Medicine (NAM)
Jan Steyaert is a Belgian bioengineer and molecular biologist. He started his career as an enzymologist but the Steyaertlab is best known for pioneering work on (engineered) nanobodies for applications in structural biology, omics and drug design. He is full professor and teaches biochemistry at the Vrije Universiteit Brussel and Director of the VIB-VUB Center for Structural Biology, one of the Research Centers of the Vlaams Instituut voor Biotechnologie (VIB). He was involved in the foundation of three spin-off companies: Ablynx, Biotalys, and Confo Therapeutics.
