All rights reserved. Genetically encodable photosensitizers based on fluorescent proteins produce reactive oxygen species when illuminated with light. Although widely used as optogenetic tools, existing photosensitizers with green fluorescence possess suboptimal properties motivating for a search of new protein variants with efficient chromophore maturation and high phototoxicity. Here we report a mutant of the phototoxic fluorescent protein KillerRed protein with fluorescence in the green part of the spectrum. The mutant variant carries mutations I64L, D114G, and T115S and does not form a DsRed-like chromophore. The protein can be used as a template to create new genetically encodable photosensitizers that are spectrally different from KillerRed.