title: Two-dimensional crystallization of the light-harvesting I-reaction centre photounit from Rhodospirillum rubrum.
abstract: A stoichiometric unit of the light-harvesting complex I and the reaction centre (LHI-RC complex) has been isolated from a carotenoid-less mutant of the purple non-sulphur bacterium Rhodospirillum rubrum by mild solubilization of photosynthetic membranes with the phospholipid detergent diheptylphosphatidylcholine. Dialysis of the isolated LHI-RC complexes in the presence of added dioleoyl-sn-phosphatidylcholine produced ordered two-dimensional crystals. Digital image processing revealed that the LHI-RC are packed together in a square lattice (a = b = 16.3 nm). The dimensions of the LHI ring are essentially identical with those determined from two-dimensional (2D) crystals of purified carotenoid-containing light-harvesting I complexes after analysis by cryo-electron microscopic techniques or from negatively stained 2D crystals of purified LHI complexes from a carotenoid-less mutant. Each LHI ring of the LHI-RC complex contains a central diffuse stain-excluding region, which is assigned to the reaction centre. The analysis of the LHI-RC 2D crystals strongly suggests that the geometry and subunit stoichiometry of the LHI ring is unaffected by the presence of a reaction centre that can probably assume various orientations within the ring.
authors.affiliation: Maurice-Müller Institute for Microscopic Structural Biology, Biozentrum, Universität Basel, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Walz
authors.forename: R
authors.initials: R
authors.lastname: Ghosh
mesh_terms: D001426:Bacterial Proteins; D002338:Carotenoids; D003460:Crystallization; D007091:Image Processing, Computer-Assisted; D045342:Light-Harvesting Protein Complexes; D008854:Microscopy, Electron; D009154:Mutation; D010713:Phosphatidylcholines; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D011487:Protein Conformation; D012247:Rhodospirillum rubrum / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D010713:Phosphatidylcholines; D045322:Photosynthetic Reaction Center Complex Proteins; C094744:light-harvesting complex 1, Rhodospirillum; D002338:Carotenoids; C017251:1,2-oleoylphosphatidylcholine