As acid levels rise, a second "cluster" involving the ECL2 loop transforms from a short hairpin into a long, protruding beta-sheet. This structural "swing" fully stabilizes the receptor in its active state. 3. Why This Matters
The video (often labeled as Video S4 in the study) demonstrates that GPR4 does not just turn "on" or "off." Instead, it follows a stepwise activation path: lfflllrr.mp4
The GPR4 receptor is a member of the G protein-coupled receptor (GPCR) family that acts as a "sensor" for extracellular acidity. This process is vital for physiological balance and is often deregulated in diseases like cancer and inflammation. As acid levels rise, a second "cluster" involving
A specific residue (H269) becomes protonated first, initiating a partial change in the receptor's shape. As acid levels rise