title: Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry?
abstract: The basic photosynthetic unit containing the reaction centre and the light-harvesting I complex (RC-LHI) of the purple non-sulphur bacterium Rhodospirillum rubrum was purified and reconstituted into two-dimensional (2D) membrane crystals. Transmission electron microscopy using conventional techniques and cryoelectron microscopy of the purified single particles and of 2D crystals yielded a projection of the RC-LHI complex at a resolution of at least 1.6 nm. In this projection the LHI ring appears to have a square symmetry and packs in a square crystal lattice. The square geometry of the LHI ring was observed also in images of single isolated particles of the RC-LHI complex. However, although the LHI units are packed identically within the crystal lattice, a new rotational analysis developed here showed that the reaction centres take up one of four possible orientations within the ring. This fourfold disorder supports our interpretation of a square ring symmetry and suggests that a hitherto undetected component may be present within the photosynthetic unit.
authors.affiliation: Biology Department, University of Lausanne (UNIL), CH-1015 Lausanne, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Stahlberg
authors.forename: J
authors.initials: J
authors.lastname: Dubochet
authors.forename: H
authors.initials: H
authors.lastname: Vogel
authors.forename: R
authors.initials: R
authors.lastname: Ghosh
mesh_terms: D020130:Bacterial Chromatophores / Q000737:chemistry; D001426:Bacterial Proteins; D020285:Cryoelectron Microscopy; D003460:Crystallization; D006863:Hydrogen-Ion Concentration; D045342:Light-Harvesting Protein Complexes; D017551:Microdialysis; D008854:Microscopy, Electron; D008970:Molecular Weight; D010742:Phospholipid Ethers; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000648:ultrastructure*; D011487:Protein Conformation; D012247:Rhodospirillum rubrum / Q000737:chemistry*; D012995:Solubility; D013057:Spectrum Analysis
chemical_list: C052298:1,2-dihexadecyl-sn-glycero-3-phosphocholine; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D010742:Phospholipid Ethers; D045322:Photosynthetic Reaction Center Complex Proteins; C094744:light-harvesting complex 1, Rhodospirillum