Monitoring the Interaction of a Single G-Protein Key Binding Site with Rhodopsin Disk Membranes upon Light Activation

Heterotrimeric G-proteins interact with their G-protein-coupled receptors (GPCRs) via key binding elements comprising the receptor-specific C-terminal segment of the alpha-subunit and the lipid anchors at the alpha-subunit N-terminus and the gamma-subunit C-terminus. Direct information about diffusion and interaction of GPCRs and their G-proteins is mandatory for all understanding of the signal transduction mechanism. By using single-particle tracking, we show that the encounters of the alpha-subunit C-terminus With the GPCR rhodopsin change after receptor activation. Slow as well as less restricted diffusion compared to the inactive state within domains 60-280 nm in length was found for the receptor-bound C-terminus, indicating short-range order in rhodopsin packing.