Kinetics of the E46Q mutant of photoactive yellow protein investigated by transient grating spectroscopy

To elucidate the role of internal proton transfer in the photodynamics of photoactive yellow protein (PYP), the photocycle of the Glu46Gln mutant of PYP (E46Q-PYP) is investigated by transient grating (TG) spectroscopy. Compared with wild-type PYP (wt-PYP), the first spectrally blue-shifted intermediate of E46Q-PYP is formed more slowly, which is consistent with the absence of direct protonation from Glu46 residue, if the parallel kinetic model for wt-PYP is invoked. The smaller conformational change in E46Q-PYP, as manifested by the smaller change in the diffusion coefficient, mainly arises from the relatively larger volume of the ground state E46Q-PYP than wt-PYP rather than from the smaller volume of the pB state.