Study on the effects of intermolecular interactions on firefly multicolor bioluminescence

Firefly luciferase exhibits a color-tuning mechanism based on pH-induced changes in the structure of the active site. These changes increase the polarity of the active site, and thus modulate the intermolecular interactions between the light emitter and active site molecules. In this study, the effects exerted by adenosine monophosphate (AMP), water molecules, and amino acids of Luciola cruciata luciferase active site on the emission wavelength of oxyluciferin were assessed by TD-DFT calculations. The redshift results mainly from decreased interaction of oxyluciferin with AMP and increased interaction of the emitter with a water molecule and Phe249. Breaking of a hydrogen bond between the benzothiazole oxygen atom with formation of a similar bond to the thiazolone oxygen atom is also instrumental.