Singlet oxygen photosensitisation by the fluorescent protein Pp2FbFP L30M, a novel derivative of Pseudomonas putida flavin-binding Pp2FbFPDedicated to Professor Kristian Berg on the occasion of his 60th birthday.Electronic supplementary information (ESI) available: Pp2FbFP L30M 1O2 phosphorescence kinetics; effect of oxygen concentration on the rate of Pp2FbFP L30M triplet state decay; transient absorbance decays; deconvolution of 1O2 phosphorescence. See DOI: 10.1039/c4pp00338a

Flavin-binding fluorescent proteins (FbFPs) are a class of fluorescent reporters that have been increasingly used as reporters in the study of cellular structures and dynamics. Flavin's intrinsic high singlet oxygen ( 1 O 2 ) quantum yield ( Φ Δ = 0.51) provides a basis for the development of new FbFP mutants capable of photosensitising 1 O 2 for mechanistic and therapeutic applications, as recently exemplified by the FbFP miniSOG. In the present work we report an investigation on the 1 O 2 photoproduction by Pp2FbFP L30M, a novel derivative of Pseudomonas putida Pp2FbFP. Direct detection of 1 O 2 through its phosphorescence at 1275 nm yielded the value Φ Δ = 0.09 ± 0.01, which is the highest 1 O 2 quantum yield reported to date for any FP and is approximately 3-fold higher than the Φ Δ for miniSOG. Unlike miniSOG, transient absorption measurements revealed the existence of two independent triplet states each with a different ability to sensitise 1 O 2 . The flavin-binding protein Pp2FbFP L30M shows a high singlet oxygen quantum yield.