Carotenoid S₁ State in a Recombinant Light-Harvesting Complex of Photosystem II

Abstract

The carotenoid species lutein, violaxanthin, and zeaxanthin are crucial in the xanthophyll-dependent nonphotochemical quenching occurring in photosynthetic systems of higher plants, since they are involved in dissipation of excess energy and thus protect the photosynthetic machinery from irreversible inhibition. Nonetheless, important properties of the xanthophyll cycle carotenoids, such as the energy of their S(1) electronic states, are difficult to study and were only recently determined in organic solvents [Polívka, T. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 4914. Frank, H. A. (2000) Biochemistry 39, 2831]. In the present study, we have determined the S(1) energies of three carotenoid species, violaxanthin, lutein, and zeaxanthin, in their LHCII (peripheral light-harvesting complex of photosystem II) protein environment by constructing recombinant Lhcb1 (Lhc = light-harvesting complex) proteins containing single carotenoid species. Within experimental error the S(1) energy is the same for all three carotenoids in the monomeric LHCII, 13,900 +/- 300 cm(-1) (720 +/- 15 nm), thus well below the Q(y)() transitions of chlorophylls. In addition, we have found that, although the S(1) lifetimes of violaxanthin, lutein, and zeaxanthin differ substantially in solution, when incorporated into the LHCII protein, their S(1) states have in fact the same lifetime of about 11 ps. Despite the similar spectroscopic properties of the carotenoids bound to the LHCII, we observed a maximal fluorescence quenching when zeaxanthin was present in the LHCII complex. On the basis of these observations, we suggest that, rather than different photochemical properties of individual carotenoid species, changes in the protein conformation induced by binding of carotenoids with distinct molecular structures are involved in the quenching phenomena associated with Lhc proteins.

Correlation of Car S1 → Chl with Chl → Car S1 Energy Transfer Supports the Excitonic Model in Quenched Light Harvesting Complex II

“…20 We compared this reconstructed spectrum with the Car S 1 transient absorption spectrum measured by Polivka and coworkers (dashed line in Figure 5) using native LHCII recorded 6 ps after excitation at 510 nm, when the internal conversion Car S 2 -Car S 1 is virtually completed. 30 Both spectra are in good agreement within the experimental noise. The differences and accuracy in the lifetime determined for a single wavelength (Figure 3b and d) or in a global analysis are comparable to or smaller than differing kinetic values reported for quenched LHCII in the literature.…”

Evidence for direct carotenoid involvement in the regulation of photosynthetic light harvesting

“…Within the experimental uncertainty, this value is identical to the intrinsic S 1 lifetime of carotenoids with 11 conjugated double bonds (23,24). Measurements of the S 1 lifetime of Zea in a variety of solvents produced a value of Ϸ9 ps (8,25), whereas recently a value of 11 ps was obtained by using a reconstituted LHCII protein with Zea as the sole carotenoid species (26). Although several other carotenoids are present in thylakoid membranes, namely ␤-carotene, Lut, Vio, and neoxanthin with intrinsic S 1 lifetimes of 9, 15, 23, and 35, respectively (8,(27)(28)(29), the data obtained from the mutants with different carotenoid composition show the generated kinetic difference is selective to Zea.…”

Energy Transfer, Excited-State Deactivation, and Exciplex Formation in Artificial Caroteno-Phthalocyanine Light-Harvesting Antennas

“…Note that in recombinant light-harvesting complex II (LHCII) with altered carotenoid pigments a similar phenomenon was observed. 25 The fifth EADS (cyan line) appears in 268 ps and does not decay on the time scale of the experiment. We observe that by now the Pc Q bleach has almost disappeared and at the same time a broad ESA between 480 and 570 nm with low amplitude has appeared.…”