Blue-light (488 nm)-irradiation-induced photoactivation of the photoactivatable green fluorescent protein

We experimentally demonstrate the photoactivatable green fluorescent protein (paGFP) photoactivation in a wavelength range where the molecule barely absorbs. The photoactivation is induced at the same wavelength used to visualize the activated form of paGFP. This can be an obstacle in the intensity evaluation in photoactivation experiments. Power and kinetics based characterization of the effect was performed in model and cell systems. This study shows an operative threshold in which paGFP is not subjected to significant photoconversion. 488 nm photoactivation is in tune with the broadening of the paGFP two-photon activation spectrum, indicating that multiple interactions lead to modifications of the molecular structure and alterations of its photophysical properties.