Exploring the Rhodopsin Dimer Interface in Live Cells

Abstract

In low-light environments, the G protein-coupled receptor (GPCR), rhodopsin, is responsible for detection of light within the retina. Several studies have shown evidence for dimeric, or oligomeric, conformations of rhodopsin within native disc membranes. However, while many oligomeric packing structures have been proposed, the exact dimerization interface of rhodopsin has yet to be firmly establish. Here we investigate rhodopsin dimerization in live cells with fluorescence correlation spectroscopy (FCS) and pulsed-interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS). One of the proposed dimerization interfaces is between TM4/5 of rhodopsin. Recently we found evidence for a similar interface in red cone opsin. Based on those previous findings, we have made point mutations along rhodopsin's TM 5, and found significant disruption of the dimerization affinity compared to the wild-type construct. Our results provide new chemical details for the previously proposed packing structure between TM 4 and 5 of rhodopsin. Moreover, our findings further support the idea of conserved dimerization interface motifs shared among class A GPCRs. Such a discovery may provide more general conceptualization of self-association among one of the largest classes of transmembrane receptors, which is essential for properly gauging the potential relationship between dimerization and function.