Understanding the energy transfer function of LHCII, the major light-harvesting complex of green plants

Since the crystal structure of the major light-harvesting complex IT (LHCII) of green plants was obtained by Kuhlbrandt, Wang and Fujiyoshi (Nature 1994, 367, 614-621), this chlorophyll-containing trimeric membrane protein has been the subject of intensive investigation. The complex contains between 36 and 42 chlorophyll molecules per trimer (Chl a and Chi b) and 10 to 12 xanthophyll molecules (lutein, neoxanthin and violaxanthin). The protein displays a rich spectrum of interactions, both between pigments and between the pigments and the protein, and these interactions have been studied with a multitude of different techniques. In this article we present an overview of the most important experimental results that have become available over the past decade and relate these to the structural knowledge. Emphasis will be put on the pigment identities, their spectroscopic features, and the interactions between the pigments, which determine both steady-state (polarized) properties and singlet and triplet energy transfer dynamics. Remaining questions will be pinpointed and hopefully they can help direct research in the near future.