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The research identifies a complex network of histidine and carboxylic acid residues on the exterior of the GPR4 receptor. Because histidines can gain a positive charge (protonate) as the environment becomes more acidic, they act as the "switch" that triggers the receptor.

A specific residue (H269) becomes protonated first, initiating a partial change in the receptor's shape. lfflllrr.mp4

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 research identifies a complex network of histidine

This research, authored by Kezheng Zhang and colleagues, provides the first structural snapshots of these "pH sensors" in action, moving from inactive to active states as they detect protons. As acid levels rise, a second "cluster" involving

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.