Multiple types of association of photosystem II and its light-harvesting antenna in partially solubilized photosystem II membranes

Photosystem II is a multisubunit pigment-protein complex embedded in the th ylakoid membranes of chloroplasts. It utilizes light for photochemical ener gy conversion, and is heavily involved in the regulation of the energy flow . We investigated the structural organization of photosystem II and its ass ociated light-harvesting antenna by electron microscopy, multivariate stati stical analysis, and classification procedures on partially solubilized pho tosystem II: membranes from spinach. Observation by electron microscopy sho rtly after a mild disruption of freshly prepared membranes with the deterge nt n-dodecyl-alpha,D-maltoside revealed the presence of several large supra molecular complexes. In addition to the previously reported supercomplexes [Boekema, E. J., van Roon, H., and Dekker, J. P. (1998) FEES Lett. 424, 95- 99], we observed complexes with the major trimeric chlorophyll a/b protein (LHCII) in a third, L-type of binding position (C2S2M0-2L1-2), and two diff erent types of megacomplexes, both identified as dimeric associations of su percomplexes with LHCII in two types of binding sites (C4S4M2-4) We conclud e that the association of photosystem II and its associated light-harvestin g antenna is intrinsically heterogeneous, and that the minor CP26 and CP24 proteins play a crucial role in the supramolecular organization of the comp lete photosystem. We suggest that different types of organization form the structural basis for photosystem II to specifically react to changing light and stress conditions, by providing different routes of excitation energy transfer.