PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

The structure bases of light harvesting and thermal dissipation in higher plant light-harvesting complex LHC-II. Zhenfeng Liu^*,1, Hanchi Yan¹, Kebin Wang², Tingyun Kuang², Jiping Zhang¹, Lulu Gui¹, Xiaomin An¹, Wenrui Chang¹, ¹ National Laboratory of Biomacromolecules, Beijing, P. R. China² Laboratory of Photosynthesis and Environmental Molecular Physiology, Beijing, P. R. China

ABSTRACT- The major light-harvesting complex (LHC-II) is the most abundant antenna complex of higher plants. It might also function in thermal dissipation of excessive energy formed under high-light conditions. In the crystal structure of spinach LHC-II at 2.72 resolution, fourteen chlorophyll molecules per monomer has been unambiguously distinguished as eight Chla and six Chlb. The orientation of the transition dipole moment of each chlorophyll has been assigned. We also revealed a characteristic chlorophyll arrangement pattern in LHC-II. The chlorophylls are distributed into two layers, each layer lying close to the stromal or lumenal surface. Within a trimeric LHC-II, 24 chlorophylls at the stromal side are organized into two irregular rings, whereas the remaining 18 chlorophylls at the lumenal side form six separate clusters. All Chlb molecules are located around the interface between adjacent monomers, and together with Chla molecules they constitute the basis for efficient light harvesting. Four carotenoid binding sites per monomeric LHC-II were observed. The close interactions of central two lutein molecules with six Chla molecules, and the interactions between neoxanthin and two Chlb molecules, indicate that these three carotenoids might serve as effective accessory light-harvesting antennae. The xanthophyll-cycle carotenoid at the monomer-monomer interface may be involved in the thermal dissipation of excessive energy, a photoprotective mechanism of plants. By correlating the structural evidences with the results of functional research, we proposed a structure-based non-photochemical quenching model.

KEY WORDS: thermal dissipation, xanthophyll-cycle carotenoid, light harvesting, crystal structure