Sandbox 173: Difference between revisions

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, inhibiting its release when hydrolyzed, thus encouraging rebinding of the Schiff base linkage<ref>Article 3</ref>.

<applet load='1u19' size='300' color='black' frame='true' align='right' caption='11-cis Retinylidene Chromophore. The generated structures are from Chain A.'/>

Rhodopsin consists of an opsin apoprotein and a <scene name='Sandbox_173/11-cis_retinylidene_structure/1'>11-cis retinylidene chromophore</scene> in its active site. Rhodopsin is bound covalently to the 11-''cis'' retinal, the chromophore or "ligand," (shown in <font color='#FFFF00'>yellow</font>) and this retinal is found in deeply in the core of the helices, in a hydrophobic site, parallel to the lipid bilayer<ref>Article 19</ref>. Comparatively, it is situated more towards the extracellular planes of the membrane bilayer <ref>Article 12</ref>. The retinal is attached in the active site of rhodopsin through a protonated Schiff base (an N-substituted imine) bond to the ε-amino group of Lysine 296 residue (shown in <font color='#00FF00'>green</font>) on the C-terminal Helix 7, with this linkage creating a positive charge on the chromophore <ref>Article 4</ref>. The protonated Schiff base of rhodopsin is stabilized through <scene name='Sandbox_173/Glu113/1'>Glutamine 113</scene> residue electrostatic interaction with the counterion, holding the inactive rhodopsin in its state<ref>Article 20</ref>.