(A) Fluorescence emission spectrum with λexc 395 nm after treatment with NH4Cl at the concentrations indicated. Values were normalized to the maximum of the water treatment. (B) Chromophore environment of crystalized cpEGFP (PDB 3EVP). The chromophore is depicted in green, the residues involved in ESPT via a buried water molecule in blue and the left linker residues GS that exchanged the LE linker, in grey. Only one linker orientation can be found, which can theoretically form weak hydrogen bonds with the chromophore (indicated distance of the hydrogen bond to the chromophore).