Conformational heterogeneity and energy transfer in photoactive proteins.

摘要

The nature of the ground and first excited states of wild type Photoactive Yellow Protein (PYP) from Halorhodospira halophila has been investigated using steady-state fluorescence and femtosecond transient absorption spectroscopy. The fluorescence spectra and fluorescence yield of PYP are temperature and excitation wavelength dependent. The fluorescence excitation spectrum is dependent on both temperature and on the emission wavelength monitored. The transient absorption spectrum is also excitation wavelength dependent. There appears to be two ground states of PYP that differ in conformation. The first ground state is blue shifted (pG_hyp) and highly fluorescent at low temperatures. The second ground state is red shifted (pG_bath) and is less fluorescent than pG_hyp. Due to these differences in fluorescence yield, pG_hyp and pG_bath differ in the yield of the photocycle at temperatures below 294 K and may have different photocycle yields at room temperature as well. Femtosecond transient absorption spectroscopy was also used to better understand the mechanism of energy transfer in reaction centers from Rhodobacter sphaeroides. Oxidizing the special pair does not inhibit energy transfer from the accessory bacteriochlorophyll B. The mutant VR(L157) does not have the Q_y transition of the special pair, and B* in VR(L157) does not decay as quickly as in wild type reaction centers.