Sandbox Reserved 1170: Difference between revisions

hGPR40 contains a highly conserved hairpin extracellular loop. This extracellular loop (<scene name='72/721541/Ecl2/4'>ECL2</scene>) is the longest and most divergent of the extracellular loops found in proteins (<scene name='72/721541/Ecl2_top/1'>top view of ECL2</scene>). The loop is accompanied by a [https://en.wikibooks.org/wiki/Structural_Biochemistry/Chemical_Bonding/_Disulfide_bonds disulfide bond] (<scene name='72/721541/Cysteine_bridge/3'>Cys79 and Cys170</scene>) that forms between transmembrane helix 4 and the C-terminus of the ECL2 loop. In hGPR40, ECL2 has two sections: a <FONT COLOR="#00FFFF">'''beta sheet'''</FONT> and an <FONT COLOR="#FF00FF">'''auxiliary loop'''</FONT>. The [https://en.wikipedia.org/wiki/Beta_sheet beta sheet] spans helices 4 and 5 and is shorter in hGPR40 than in other GPCRs. The ECL2 of hGPR40 also differs from that of other proteins because it contains an auxiliary loop of 13 extra residues. The entire extracellular loop has low mobility and flexibility which allows it to act as a cap for the binding pocket. The only exception to the low flexibility is the tip of the auxiliary loop, which corresponds to residues Asp152-Asn155. This area of greater mobility allows for substrates to enter the binding site.<ref name="Srivastava"/>