Pump-probe anisotropies of Fenna-Matthews-Olson protein trimers from Chlorobium tepidum: a diagnostic for exciton localization?

AUTOR(ES)

Savikhin, S

RESUMO

Exciton calculations on symmetric and asymmetric Fenna-Matthews-Olson (FMO) trimers, combined with absorption difference anisotropy measurements on FMO trimers from the green bacterium Chlorobium tepidum, suggest that real samples exhibit sufficient diagonal energy disorder so that their laser-excited exciton states are noticeably localized. Our observed anisotropies are clearly inconsistent with 21-pigment exciton simulations based on a threefold-symmetric FMO protein. They are more consistent with a 7-pigment model that assumes that the laser-prepared states are localized within a subunit of the trimer. Differential diagonal energy shifts of 50 cm(-1) between symmetry-related pigments in different subunits are large enough to cause sharp localization in the stationary states; these shifts are commensurate with the approximately 95 cm(-1) inhomogeneous linewidth of the lowest exciton levels. Experimental anisotropies (and by implication steady-state linear and circular dichroism) likely arise from statistical averaging over states with widely contrasting values of these observables, in consequence of their sensitivity to diagonal energy disorder.

Documentos Relacionados

• Ultrafast absorption difference spectra of the Fenna-Matthews-Olson protein at 19 K: experiment and simulations.
• Fluorescence lifetime imaging by asynchronous pump-probe microscopy.
• Femtosecond pump-probe spectroscopy of bacteriochlorophyll a monomers in solution.
• Malate dehydrogenase from the mesophile Chlorobium vibrioforme and from the mild thermophile Chlorobium tepidum: molecular cloning, construction of a hybrid, and expression in Escherichia coli.
• Crystal structures of photosynthetic reaction center and high-potential iron-sulfur protein from Thermochromatium tepidum: Thermostability and electron transfer