title: Multiple crystal types reveal photosystem II to be a dimer.
abstract: Three types of photosystem II (PS II) crystals have been produced using a variety of detergents. Intermediate stages of crystal formation were examined and it was determined that each crystal probably originates from a single grana membrane. Each crystal type was examined by electron microscopy and image processing, providing three different projection maps. The highest resolution results came from type 1 and type 2 crystals. Projection maps from these crystals were examined for two-fold symmetry via difference maps between the unsymmetrized averages and their 180 degrees rotation. A comparison of the final maps shows a high degree of two-fold symmetry, with only slight differences noted in the low density regions of the two halves of the structure. The interpretation is that PS II is a dimer, with the further suggestion that the two reaction center cores may have slightly different complements of antennae polypeptides.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Campus Box 347, University of Colorado, Boulder, CO 80307, USA. mkl@demeter.colorado.edu
authors.forename: M K
authors.initials: MK
authors.lastname: Lyon
mesh_terms: D003460:Crystallization; D019281:Dimerization; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex