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Abstract

Assemblies of Photosystem II and light-harvesting proteins were purified from the liverwort Marchantia polymorpha and investigated by two- and three-dimensional transmission electron microscopy of negatively stained specimens. By single-particle analysis, it was determined that about 25% of the particles are rectangular or slightly S-shaped with dimensions of 285 Å in length, 144 Å in width, 84 Å in height, while the membrane part is about 52 Å thick. This structure reveals the same architecture as that of a Photosystem II-light-harvesting assembly from seed plants. An overlay of the projection structure of the liverwort's complex with a projection structure deduced from stained trimeric LHC II crystals from pea confirmed the locations of trimeric LHC II within the liverwort's complex. Remarkably tight associations of LHC II and other chlorophyll a/b binding proteins with the PS II core complex are observed. More than 50% of the Photosystem II particles from the liverwort carry one or two additional masses. These extra masses are found to consist of an additional LHC II trimer and probably a chlorophyll a/b binding protein. For the first time, a three-dimensional structure of such a large assembly is defined.