GPCR activation: protonation and membrane potential EVIEW R

GPCR proteins represent the largest family of signaling membrane proteins in eukaryotic cells. Their importance to basic cell biology, human diseases, and pharma- ceutical interventions is well established. Many crystal structures of GPCR proteins have been reported in both active and inactive conformations. These data indicate that agonist binding alone is not suffi cient to trigger the conformational change of GPCRs necessary for binding of downstream G-proteins, yet other essential factors re- main elusive. Based on analysis of available GPCR crystal structures, we identifi ed a potential conformational switch around the conserved Asp2.50, which consistently shows distinct conformations between inactive and active states. Combining the structural information with the current literature, we propose an energy-coupling mechanism, in which the interaction between a charge change of the GPCR protein and the membrane potential of the living cell plays a key role for GPCR activation.