User:Brittany Stankavich/Sandbox 1

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User:Brittany Stankavich/Sandbox 1

hGPR40 Homo sapiens

Image:GPR40 TAK.png

1 Introduction
2 Function
3 Signal Transduction
- 3.1 Ligand Binding
  - 3.1.1 Free Fatty Acids
  - 3.1.2 TAK-875
- 3.2 Binding Pockets
4 Medical Relevance

Introduction

Human GPR40 receptor, hGPR40, is a free fatty-acid receptor that binds to long chain free fatty acids, inducing insulin secretion. However, what makes this receptor significant is that the secretion of insulin is glucose dependent. Thus, there needs to be an agonist bound, in addition to presence of glucose in the blood in order for insulin secretion to occur. This glucose-dependence makes GPR40 a target for type-2 diabetes because it allows for increased glycemic control and therefore, low risk of hypoglycemia.

Function

Signal Transduction

FFAs bind to GPR40 which then couples with the G-protein Gq leading to increased phospholipase C (PLC) activity. PLC catalyzes the hydrolysis of the phospholipid phosphatidylinositol-4,5-biphosphate (PIP2) resulting in the formation of diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). DAG can activate protein kinase C (PKC) to enhance insulin secretion. IP3 on the other hand is soluble and diffuses to the endoplasmic reticulum where it is able to bind to a receptor on a ligand-gated Ca2+ channel. This binding triggers the opening of the channel causing stored Ca2+ to be released into the cytoplasm. Upon this large increase in intracellular free Ca2+, there is also an increase in glucose-dependent insulin secretion suggesting that insulin release can be contributed in part to the changes in Ca2+ concentration resulting from activated GPR40 ^[1].

Ligand Binding

Free Fatty Acids

GPR40’s natural substrate are FFAs in which a free carboxyl group is required to bind. However, GPR40 can be activated by a wide variety of fatty acids with chain lengths ranging from saturated fatty acids with 8 carbons to 23 carbons. In addition, various mono (i.e. palmitoleic (C16:1) and oleic (C18:1) acids) and poly-unsaturated fatty acids (i.e. linoleic (C18:2) and eicosatrienoic (C20:3) acids) can activate GPR40 (Morgan et al. 2009). The agonists potency varies according to the carbon-chain length however. The activity of GPR40 increases when the chain is increased from C6 to C15 but then decreased when the chain was extended beyond C15. One explanation for this is that as alkyl chain increased, so did the hydrophobic interactions with the protein within the binding pocket. However, for FFAs with carbon chains longer than C15, the molecular size is too large for the binding pocket. This causes the alkyl chain to extend beyond the binding pocket and destabilize the binding ^[2].

FFAs bind to hGPR40 by coordinating its free carboxyl group to three amino acids, Arg183, Asn244, and Arg258, which are located close to the of hGPR40 on TM5, 6 and 7. Because of the close proximity of these residues to the extracellular domain and the dominantly hydrophobic nature of FFA’s, it is possible that ligand binding occurs close to, or within, the plane of the membrane ^[1].

TAK-875

Tak-875 is known to be a partial agonist of GPR40. The bonding of this ligand to the bonding site is fairly unique, as it is proposed that the ligand must enter through the membrane bilayer. This is performed via a method similar to ligand binding to sphingosine 1-phosphate receptor 1 3v2w, retinal loading of opsin 4j4q and the entry of anandamide in cannabinoid receptors, in which extracellular loops block the binding from the extracellular matrix ^[3]. In contrast, delta opioid receptor binding 4ej4 allow for binding directly from the extracellular matrix. The binding mechanism through the bilayer may be selectively favoring the free fatty acid because of the non-polar regions of the ligand.

The carboxylic acid terminus of TAK-875 is buried within a very hydrophobic region where it interacts with polar residues Arg 183, Arg 258, Tyr 91, and Tyr 240.

Image:Binding.jpg

TAK-875 binding pocket buried within hydrophobic region

Binding Pockets

Medical Relevance

While undergoing clinical trials, the use of TAK-875 in the treatment of diabetes mellitus was terminated in the III phase. This was due to observed liver toxicity. The liver toxicity is believed to be due to its effects on the bile acids, achieved through the inhibition of the efflux of bile acids into bile ^[4]. Other molecules are currently undergoing development in an effort to activate hGPR40 in a way that does not adversely affect the liver. The leading research suggests a molecule similar to that of 3-ethoxypropanoic acid ^[5]. However, this molecule must be modified before it could be conceivably used, as its half-life is extremely short, due to the rapid oxidation at the benzyl position during metabolism ^[5]

References

↑ ^1.0 ^1.1 Morgan NG, Dhayal S. G-protein coupled receptors mediating long chain fatty acid signalling in the pancreatic beta-cell. Biochem Pharmacol. 2009 Dec 15;78(12):1419-27. doi: 10.1016/j.bcp.2009.07.020., Epub 2009 Aug 4. PMID:19660440 doi:http://dx.doi.org/10.1016/j.bcp.2009.07.020
↑ Ren XM, Cao LY, Zhang J, Qin WP, Yang Y, Wan B, Guo LH. Investigation of the Binding Interaction of Fatty Acids with Human G Protein-Coupled Receptor 40 Using a Site-Specific Fluorescence Probe by Flow Cytometry. Biochemistry. 2016 Mar 17. PMID:26974599 doi:http://dx.doi.org/10.1021/acs.biochem.6b00079
↑ Hanson MA, Roth CB, Jo E, Griffith MT, Scott FL, Reinhart G, Desale H, Clemons B, Cahalan SM, Schuerer SC, Sanna MG, Han GW, Kuhn P, Rosen H, Stevens RC. Crystal structure of a lipid G protein-coupled receptor. Science. 2012 Feb 17;335(6070):851-5. PMID:22344443 doi:10.1126/science.1215904
↑ Li X, Zhong K, Guo Z, Zhong D, Chen X. Fasiglifam (TAK-875) Inhibits Hepatobiliary Transporters: A Possible Factor Contributing to Fasiglifam-Induced Liver Injury. Drug Metab Dispos. 2015 Nov;43(11):1751-9. doi: 10.1124/dmd.115.064121. Epub 2015, Aug 14. PMID:26276582 doi:http://dx.doi.org/10.1124/dmd.115.064121
↑ ^5.0 ^5.1 Takano R, Yoshida M, Inoue M, Honda T, Nakashima R, Matsumoto K, Yano T, Ogata T, Watanabe N, Hirouchi M, Yoneyama T, Ito S, Toda N. Discovery of DS-1558: A Potent and Orally Bioavailable GPR40 Agonist. ACS Med Chem Lett. 2015 Jan 13;6(3):266-70. doi: 10.1021/ml500391n. eCollection, 2015 Mar 12. PMID:25815144 doi:http://dx.doi.org/10.1021/ml500391n

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Brittany Stankavich

Retrieved from "http://52.214.119.220/wiki/index.php/User:Brittany_Stankavich/Sandbox_1"

@@ Line 19: / Line 19: @@
 [[Image:Gpr40 insulin pathway.png|400 px|center|hGPR40]]
-FFAs bind to GPR40 which then couples with the G-protein Gq leading to increased phospholipase C (PLC) activity. PLC catalyzes the hydrolysis of the phospholipid phosphatidylinositol-4,5-biphosphate (PIP2) resulting in the formation of diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). DAG can activate protein kinase C (PKC) to enhance insulin secretion. IP3 on the other hand is soluble and diffuses to the endoplasmic reticulum where it is able to bind to a receptor on a ligand-gated Ca2+ channel. This binding triggers the opening of the channel causing stored Ca2+ to be released into the cytoplasm. Upon this large increase in intracellular free Ca2+, there is also an increase in glucose-dependent insulin secretion suggesting that insulin release can be contributed in part to the changes in Ca2+ concentration resulting from activated GPR40.
+FFAs bind to GPR40 which then couples with the G-protein Gq leading to increased phospholipase C (PLC) activity. PLC catalyzes the hydrolysis of the phospholipid phosphatidylinositol-4,5-biphosphate (PIP2) resulting in the formation of diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). DAG can activate protein kinase C (PKC) to enhance insulin secretion. IP3 on the other hand is soluble and diffuses to the endoplasmic reticulum where it is able to bind to a receptor on a ligand-gated Ca2+ channel. This binding triggers the opening of the channel causing stored Ca2+ to be released into the cytoplasm. Upon this large increase in intracellular free Ca2+, there is also an increase in glucose-dependent insulin secretion suggesting that insulin release can be contributed in part to the changes in Ca2+ concentration resulting from activated GPR40 <ref name="Morg">PMID:19660440</ref>.
-== Structure ==
 <scene name='72/727085/Hgpr40_a/6'>Extracellular loop 2 (ECL2)</scene>
-hGPR40 possesses seven <scene name='72/727085/Hgpr40_transmembrane/2'>transmembrane domains</scene> characteristic of G protein-coupled receptors.
 === Ligand Binding ===
-GPR40’s natural substrate are FFAs in which a free carboxyl group is required to bind. However, GPR40 can be activated by a wide variety of fatty acids with chain lengths ranging from saturated fatty acids with 8 carbons to 23 carbons. In addition, various mono (i.e. palmitoleic (C16:1) and oleic (C18:1) acids) and poly-unsaturated fatty acids (i.e. linoleic (C18:2) and eicosatrienoic (C20:3) acids) can activate GPR40 (Morgan et al. 2009). The agonists potency varies according to the carbon-chain length however. The activity of GPR40 increases when the chain is increased from C6 to C15 but then decreased when the chain was extended beyond C15. One explanation for this is that as alkyl chain increased, so did the hydrophobic interactions with the protein within the binding pocket. However, for FFAs with carbon chains longer than C15, the molecular size is too large for the binding pocket. This causes the alkyl chain to extend beyond the binding pocket and destabilize the binding (Ren et al. 2016).
+==== Free Fatty Acids ====
+GPR40’s natural substrate are FFAs in which a free carboxyl group is required to bind. However, GPR40 can be activated by a wide variety of fatty acids with chain lengths ranging from saturated fatty acids with 8 carbons to 23 carbons. In addition, various mono (i.e. palmitoleic (C16:1) and oleic (C18:1) acids) and poly-unsaturated fatty acids (i.e. linoleic (C18:2) and eicosatrienoic (C20:3) acids) can activate GPR40 (Morgan et al. 2009). The agonists potency varies according to the carbon-chain length however. The activity of GPR40 increases when the chain is increased from C6 to C15 but then decreased when the chain was extended beyond C15. One explanation for this is that as alkyl chain increased, so did the hydrophobic interactions with the protein within the binding pocket. However, for FFAs with carbon chains longer than C15, the molecular size is too large for the binding pocket. This causes the alkyl chain to extend beyond the binding pocket and destabilize the binding <ref name="Ren">PMID:26974599</ref>.
+FFAs bind to hGPR40 by coordinating its free carboxyl group to three amino acids, Arg183, Asn244, and Arg258, which are located close to the <scene name='72/727085/Hgpr40_transmembrane/2'>extracellular domains</scene> of hGPR40 on TM5, 6 and 7. Because of the close proximity of these residues to the extracellular domain and the dominantly hydrophobic nature of FFA’s, it is possible that ligand binding occurs close to, or within, the plane of the membrane <ref name="Morg">PMID:19660440</ref>.
+==== TAK-875 ====
 '''Tak-875''' is known to be a [https://en.wikipedia.org/wiki/Partial_agonist partial agonist] of GPR40. The bonding of this ligand to the bonding site is fairly unique, as it is proposed that the ligand must enter through the [https://en.wikipedia.org/wiki/Cell_membrane membrane bilayer]. This is performed via a method similar to ligand binding to sphingosine 1-phosphate receptor 1 [[:3v2w]], retinal loading of opsin [[:4j4q]] and the entry of anandamide in [https://en.wikipedia.org/wiki/Cannabinoid_receptor cannabinoid receptors], in which extracellular loops block the binding from the extracellular matrix <ref>PMID:22344443</ref>. In contrast, delta opioid receptor binding [[:4ej4]] allow for binding directly from the [https://en.wikipedia.org/wiki/Extracellular_matrix extracellular matrix]. The binding mechanism through the bilayer may be selectively favoring the free fatty acid because of the [https://en.wikipedia.org/wiki/Chemical_polarity#Nonpolar_molecules non-polar] regions of the ligand.