title: Highly ordered two-dimensional crystals of photosystem I reaction center from Synechococcus sp.: functional and structural analyses.
abstract: The photosystem 1 reaction center complex from the thermophilic cyanobacterium Synechococcus sp. was isolated by Triton X-100 solubilization and fractional precipitation with polyethylene glycol. As shown by gel electrophoresis, the isolated complex was composed of the 83 kDa subunits A and B, and at least six other subunits with molecular mass below 20 kDa. Electron transfer from the primary electron donor P700 to the FA/FB centers was demonstrated by flash-induced absorption change of the isolated complex, while electron paramagnetic resonance (EPR) spectroscopy showed that the complex contained a full set of Fe-S clusters. Isolated complexes were reconstituted into two-dimensional crystals in the presence of phospholipids and different cations. The crystals were found to be active by flash-induced separation and EPR spectroscopy. Electron microscopy and digital image processing of negatively stained and frozen-hydrated specimens revealed orthorhombic crystals with unit cell dimensions a = 138 A, b = 145 A and p12(1) symmetry. A three-dimensional map was calculated for negatively stained crystals to 19 A resolution, whereas the projection map of frozen-hydrated crystals exhibited 8 A resolution.
authors.affiliation: M. E. Müller Institute for Microscopic Structural Biology, University of Basel, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Karrasch
authors.forename: D
authors.initials: D
authors.lastname: Typke
authors.forename: T
authors.initials: T
authors.lastname: Walz
authors.forename: M
authors.initials: M
authors.lastname: Miller
authors.forename: G
authors.initials: G
authors.lastname: Tsiotis
authors.forename: A
authors.initials: A
authors.lastname: Engel
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005615:Freezing; D007091:Image Processing, Computer-Assisted; D008051:Lipid Bilayers; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008854:Microscopy, Electron / Q000379:methods; D008956:Models, Chemical; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D012995:Solubility
chemical_list: D008051:Lipid Bilayers; D008055:Lipids; D045322:Photosynthetic Reaction Center Complex Proteins