User:Daniel Schemenauer/Sandbox 1: Difference between revisions

G-coupled protein receptors [https://en.wikipedia.org/wiki/G_protein–coupled_receptor (GPCR's)] are helical trans-membrane proteins that bind to an extracellular signal and activate a cellular response.  The human genome encodes for approximately 750 GPCR's, 350 of which are known to respond to extracellular ligands.<ref name="GPCRRep">PMID: 12679517 </ref>  GPCR's are divided into four major classes based on sequence similarity and transduction mechanism: Class A,B,C, and F.<ref name="MSGPCR">PMID:23407534</ref>  Metabotropic Glutamate Receptor 5 (<scene name='72/726409/Overview/5'>mGlu₅</scene>) is a class C GPCR that is involved in the G_q pathway.<ref name="CCGPCR">PMID:12782243</ref>  In this pathway, glutamate binds to the extracellular domain of mGlu₅, and the trans-membrane domains then undergo a conformational change that activates the coupled [http://proteopedia.org/wiki/index.php/GTP-binding_protein G-protein] on the intracellular side of the membrane.<ref name="Primary">PMID: 25042998 </ref>  The activated G-protein disassociates, and the alpha subunit activates [https://en.wikipedia.org/wiki/Phospholipase_C Phospholipase C].  Phospholipase C in turn cleaves [https://en.wikipedia.org/wiki/Phosphatidylinositol_4,5-bisphosphate PIP2] to [https://en.wikipedia.org/wiki/Diglyceride DA] and [https://en.wikipedia.org/wiki/Inositol_trisphosphate IP3].  IP3 then binds to calcium channels on the [https://en.wikipedia.org/wiki/Endoplasmic_reticulum Endoplasmic reticulum] creating an increased cellular concentration of calcium.  Increased calcium concentrations thus lead to increased neuronal activity.<ref name="MSGPCR">PMID:23407534</ref>  Due to its involvement in neuronal activity, mGlu₅ is highly expressed in neuronal and glial cells in the central nervous system, where glutamate serves as the major neurotransmitter.  

A number of intramolecular interactions within the trans-membrane domain stabilize the inactive conformation of mGlu₅, as demonstrated by <scene name='72/726409/Overview/5'>mGlu₅</scene> being represented in the inactivate state.  While in the inactive state, glutamate binding to mGlu₅ triggers a conformational change that leads to mGlu₅ to be in the active state and hence triggers the aforementioned [https://en.wikipedia.org/wiki/Gq_alpha_subunit G_q pathway].  The first of these interactions is an ionic interaction, termed the <scene name='72/726409/Ionic_lock2/2'>Ionic Lock</scene>, between Lysine 665 of TM3 and Glutamate 770 of TM6.  Evidence for the importance of this interaction came through a kinetic study of mutant proteins where both residues were separately substituted with alanine, resulting in constitutive activity of the GPCR and its coupled pathway.<ref name="Primary">PMID: 25042998 </ref>  A second critical interaction that stabilizes the inactive conformer is a <scene name='72/726409/Hydrogen_bond_614-668/2'>Hydrogen Bond </scene> between Serine 614 of ICL1 and Arginine 668 of TM3. Similarly, when Serine 614 was substituted with alanine, high levels of activity were seen in the mutant GPCR.<ref name="Primary">PMID: 25042998 </ref>  A <scene name='72/726404/Scene_6/10'>Disulfide Bond </scene> between Cysteine 644 of TM3 and Cysteine 733 of <scene name='72/726409/Mavoglurant_overview2/5'>ECL2</scene> is critical at anchoring ECL2 and is highly conserved across Class C GPCR’s.<ref name="Primary">PMID: 25042998 </ref>  The ECL2's presence combined with the helical bundle of the trans-membrane domain creates a <scene name='72/726409/Electrogradient2/9'>Binding Cap</scene> that restricts entrance to the allosteric binding site within the seven trans-membrane α-helices.  This restricted entrance has no effect on the natural ligand, glutamate, as it binds to the extracellular domain, but this entrance dictates potential drug targets that act through allosteric modulation.<ref name="Primary">PMID: 25042998 </ref>  

The bicyclic ring system of the drug is surrounded by a pocket of mainly hydrophobic residues including Val 806, Met 802, Phe 788, Trp 785, Leu 744, Ile 651, Pro 655, and Asn 747 (Figure 1).<ref name="Primary">PMID: 25042998 </ref>  The carbamate tail of Mavoglurant forms a hydrogen bond through its carbonyl oxygen to the amide side-chain of Asparagine 747 of TM4 (Figure 2). A hydroxyl group similarly forms hydrogen bonds to mGlu₅, specifically at two serine residues (S805 and S809) of TM7.  These residues form a hydrogen bonding network to other residues through their main chain atoms and a coordinated water molecule. The interactions between Mavoglurant and mGlu₅ involve TM helices that were not previously stabilized by any strong interactions, introducing a new level of stability that favors the inactive conformation of the protein and hence decreases the overall activity of mGlu₅.<ref name="Primary">PMID: 25042998 </ref>   

Mavoglurant was met by disappointing Fragile X Syndrome trial results and ultimately discontinued for Fragile X Syndrome in 2014, but testing for dyskinesia and [https://en.wikipedia.org/wiki/Obsessive%E2%80%93compulsive_disorder Obsessive-compulsive disorder] are still in progress. [https://en.wikipedia.org/wiki/Basimglurant Basimglurant] and [https://en.wikipedia.org/wiki/MTEP MTEP] are inhibitors that are similar to Mavoglurant as they both function as negative allosteric modulators to mGlu₅, and they are currently under trials to serve as medications for depression.<ref name="Clinical">PMID: 26219727 </ref><ref name=”Clinical2”>PMID: 25043733 </ref>