A Genetically-Encoded YFP Sensor with Enhanced Chloride Sensitivity, Photostability and Reduced pH Interference Demonstrates Augmented Transmembrane Chloride Movement by Gerbil Prestin (SLC26a5)
Figure 4
The H-bond network comprising the proton transfer pathway within the chromophore (in Yellow) of YFP-H148Q drawn with PyMol.
Water molecules displayed as red balls. (A) YFP-H148Q without halide-binding (PDB: 1F0B). The phenolic oxygen of the chromophore is H-bonded to a water molecule that is also H-bonded to the side chain of S205 and the main chain of N146; additionally, there is a H-bond to a surface water molecule that is exposed to exterior solvent. E222 is H-bonded to the nitrogen on the imidazole ring, indicating that E222 is protonated, while the phenolic group of Y203 forms H-bond with Q69 and a nearby water molecule. Notably, there is no H-bond between S205 and E222 whose nearest distance is 3.9 Å. (B) iodide-bound YFP-H148Q (PDB: 1F09). The water molecule H-bonded to N146, S205 and the phenolic oxygen of the chromophore was separated away from the surface water molecule, whose distance increased to 4.7 Å. The deprotonated E222 forms H-bond to S205 that is in the H-bond chain with protonated chromophore, while the phenolic group of Y203 is near H-bonding distance with iodide, which may be a reason why YFPs are halide-sensitive since Y203 is the unique residue of YFP from GFP.