Sandbox 173: Difference between revisions

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Andrea Gorrell, Cinting Lim

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 ===G Protein-Coupled Receptors===
-Rhodopsin is a member of the superfamily of G protein-coupled receptors that incorporate the activation of G proteins in their modulation of signalling and intracellular actions. Rhodopsin shares similar membrane topology with the members of the superfamily (Family A of the G protein-coupled receptors) which include the seven transmembrane helices, an extracellular N terminus and cytoplasmic C terminus<ref>Article 20</ref>. The seven-helical pattern is found from archaebacteria (specifically studied is bacteriorhodopsin) to humans, both which share the same retinylidene chromophore as well <ref>Article 12</ref>. As the crystal structure for any G protein-coupled receptor with the seven transmembrane domain has only been solved for rhodopsin, rhodopsin may act as a reference for the structure and function relationship for other G protein-coupled receptors<ref>Article 20</ref>. Like most G protein-coupled receptors, the activated rhodopsin catalyzes uptake of GTP by the heterotrimeric G protein, in this case [http://en.wikipedia.org/wiki/Transducin transducin], which interacts with the cytoplasmic loops of the receptor<ref>Article 10</ref>. However, the covalent binding nature of rhodopsin to its retinal ligand is unlike most G protein-coupled receptors. As well, another difference of rhodopsin from the members of this superfamily relates to light as the inducer for activation<ref>Article 20</ref>.
+Rhodopsin is a member of the superfamily of G protein-coupled receptors that incorporate the activation of G proteins in their modulation of signalling and intracellular actions. Rhodopsin shares similar membrane topology with the members of the superfamily (Family A of the G protein-coupled receptors) which include the seven transmembrane helices, an extracellular N terminus and cytoplasmic C terminus<ref>Article 20</ref>. The seven-helical pattern is found from archaebacteria (specifically studied is bacteriorhodopsin) to humans, both which share the same retinylidene chromophore as well <ref>Article 12</ref>. As the crystal structure for any G protein-coupled receptor with the seven transmembrane domain has only been solved for rhodopsin, rhodopsin may act as a reference for the structure and function relationship for other G protein-coupled receptors<ref>Article 20</ref>. Like most G protein-coupled receptors, the activated rhodopsin catalyzes uptake of GTP by the heterotrimeric G protein, in this case [http://en.wikipedia.org/wiki/Transducin transducin], which interacts with the cytoplasmic loops of the receptor<ref name="Article10">PMID:11698103</ref>. However, the covalent binding nature of rhodopsin to its retinal ligand is unlike most G protein-coupled receptors. As well, another difference of rhodopsin from the members of this superfamily relates to light as the inducer for activation<ref>Article 20</ref>.
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 <scene name='Sandbox_173/Cys322_and_cys323/1'>Cysteine 322 and Cysteine 323</scene>, which are <scene name='Sandbox_173/Palmitates/3'>palmitoylated</scene>. This helix runs approximately parallel to the cytoplasmic surface and is involved in Gtγ binding<ref name="Article9"/>, as well as the modulation of rhodopsin-transducin interactions and rhodopsin-phospholipid interactions<ref>Article 12</ref>.
-A metal zinc ion bridge chelated by histidine side-chains and connected to the cytoplasmic ends of Helix 3 and 6 is observed to prevent receptor activation. This perhaps indicates that separation of these cytoplasmic ends would contribute to rhodopsin activation<ref>Article 10</ref>.
+A metal zinc ion bridge chelated by histidine side-chains and connected to the cytoplasmic ends of Helix 3 and 6 is observed to prevent receptor activation. This perhaps indicates that separation of these cytoplasmic ends would contribute to rhodopsin activation<ref name="Article10"/>.
 The structure of rhodopsin may provide stability to the important Schiff base linkage with the retinal by affecting its hydrolysis, limiting its interactions with solvent, and inhibiting its release when hydrolyzed, thus encouraging rebinding of the Schiff base linkage<ref name="Article3">PMID:14611935</ref>.
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 ====Adjustment and Thermal Relaxation of the Protein====
-Upon activation, movement and slight adjustment of helices are observed, with the inner faces of Helix 2, 3, 6 and 7 becoming more exposed<ref>Article 10</ref>. As Helices 3 and 6 move outward, the binding site for transducin is more accessible as there is opening between cytoplasmic loops<ref>Article 19</ref>.
+Upon activation, movement and slight adjustment of helices are observed, with the inner faces of Helix 2, 3, 6 and 7 becoming more exposed<ref name="Article10"/>. As Helices 3 and 6 move outward, the binding site for transducin is more accessible as there is opening between cytoplasmic loops<ref>Article 19</ref>.
 Following activation, a slower thermal relaxation process occurs. This involves conformational changes in the retinal and opsin to result in fully active Metarhodopsin II<ref name="Article6"/>.