Spectral Features and Excited State Dynamics of Carotenoid in B800-Depleted Light-Harvesting Complex 2

Carotenoid plays important roles in both photon capture and photoprotection in photosynthetic light-harvesting (LH) proteins. Chemically modified LH proteins will expand our knowledge of the photofunctional roles of carotenoids. Here, we investigate spectral properties of carotenoid and energy transfer dynamics concerning photoprotection in LH2 that lacks B800 bacteriochlorophyll (BChl) <i>a</i> (B800-depleted LH2). B800-depleted LH2 produced a blue shift of the absorption band of carotenoid in LH2. Resonance Raman spectroscopy indicated alteration of the geometric distortion of the conjugated polyene chain of the bound carotenoid by the B800 removal. The distortion of the carotenoid chain in B800-depleted LH2 would contribute to the blue shift of the carotenoid absorption. The B800 removal induced the rapid generation of the T₁ state of carotenoid by excitation of B850 BChl <i>a</i>. The new energy flow pathway may serve as an alternative photoprotection mechanism, preventing the formation of the B850 T₁ state.