Energy Transfers in the B808–866 Antenna from the Green Bacterium Chloroflexus aurantiacus

Abstract

Energy transfers within the B808-866 BChl a antenna in chlorosome-membrane complexes from the green photosynthetic bacterium Chloroflexus aurantiacus were studied in two-color pump-probe experiments at room temperature. The steady-state spectroscopy and protein sequence of the B808-866 complex are reminiscent of well-studied LH2 antennas from purple bacteria. B808-->B866 energy transfers occur with approximately 2 ps kinetics; this is slower by a factor of approximately 2 than B800-->B850 energy transfers in LH2 complexes from Rhodopseudomonas acidophila or Rhodobacter sphaeroides. Anisotropy studies show no evidence for intra-B808 energy transfers before the B808-->B866 step; intra-B866 processes are reflected in 350-550 fs anisotropy decays. Two-color anisotropies under 808 nm excitation suggest the presence of a B808-->B866 channel arising either from direct laser excitation of upper B866 exciton components that overlap the B808 absorption band or from excitation of B866 vibronic bands in nontotally symmetric modes.

Excitation energy transfer and trapping dynamics in the core complex of the filamentous photosynthetic bacterium Roseiflexus castenholzii

“…sphaeroides; our findings substantiate a circular model for the LHB800-880-RC assembly such that the circle of about 32 ± 1 interacting BChl a molecules are coupled to the low exciton transition of the reaction center primary donor P . This arrangement is similar to that proposed in the work of Novoderezhkin et al (1998). A similar circular arrangement of the LH antenna around the RC in Rf.…”

“…One model for the light-harvesting antenna LHB808-866 complex of Cf. aurantiacus has been proposed by Novoderezhkin et al (1998). In that model, two concentric aggregates are considered that lie in two planes parallel to the membrane plane; the first consists of 24-32 BChl 866 strongly coupled molecules, in which the strongest interactions are between dimers, the second ring consists of 12-18 BChl 808 weakly coupled molecules.…”

“…Previous studies suggest that the building blocks of the LHB808-866 antenna from Cf. aurantiacus spectrally similar to LH2 complexes from purple bacteria, but topologically similar to LH1 complexes (Feick et al 1995;Novoderezhkin et al 1998;Xin et al 2005;Collins et al 2009Collins et al , 2010. The physiological significance of this mosaic antenna is yet to be revealed.…”

Purification and Characterization of the B808–866 Light-harvesting Complex from Green Filamentous Bacterium Chloroflexus aurantiacus

“…The energy transfer between the 808 and 866 nm bands was studied by picosecond fluorescence decay and was found to have an equilibration time of 5 ps (Griebenow et al 1991). The results obtained by femtosecond differential absorption study showed that this energy transfer occurs with $2 ps kinetics in whole chlorosome-membrane complexes (Novoderezhkin et al 1998). We have recently investigated the excitation energy transfer processes between the carotenoids and BChls in isolated core complexes (Montan˜o et al 2004) and found that the low efficiency of energy transfer is probably due to that only the carotenoid S 1 excited state is involved.…”

Orientation of B798 BChl a Q y transition dipoles in Chloroflexus aurantiacus chlorosomes: polarized transient absorption spectroscopy studies

“…Moreover, our earlier pump-probe experiments on CMC, isolated from the similar Cfx. aurantiacus cell culture C-8, strongly suggest that the entire BChl a band with absorption maximum at *805 nm (which is a superposition of the B798 and B808 BChl a bands) is due to pigments, functioning essentially as monomeric ones (Novoderezhkin et al 1998b). In addition, the shape of the BChl a DA spectrum fully reproduces the shape of the B798 steady-state absorption spectrum.…”