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Role of Conserved Transmembrane Domain Cysteines in Activation of Metabotropic Glutamate Receptor Subtype 6

Abstract

Kalyan C Tirupula, Harpreet Kaur Dhiman, Leelavati Murthy, Alessandro Bisello and Judith Klein-Seetharaman

Metabotropic glutamate receptor subtype 6 (mGluR6) is a Class C type G protein coupled receptor (GPCR) uniquely expressed on retinal bipolar cells. mGluR6 plays a key role in dim-light vision but little is known about its structure and function. Here, we characterized the role of the three transmembrane (TM) cysteines in activation through site-directed mutagenesis. Function of the receptors in cells and membranes was assayed using cAMP and G protein activation, respectively. Cysteine mutants in TM helix V displayed slightly elevated or wild-type like activity. In contrast, all mutations involving the cysteine in TM helix VI lacked agonist response. Our results suggest that TM VI plays a key role in Class C activation similar to that observed in rhodopsin-like (Class A) GPCRs.