title: Structure of the dimeric PufX-containing core complex of Rhodobacter blasticus by in situ atomic force microscopy.
abstract: We have studied photosynthetic membranes of wild type Rhodobacter blasticus, a closely related strain to the well studied Rhodobacter sphaeroides, using atomic force microscopy. High-resolution atomic force microscopy topographs of both cytoplasmic and periplasmic surfaces of LH2 and RC-LH1-PufX (RC, reaction center) complexes were acquired in situ. The LH2 is a nonameric ring inserted into the membrane with the 9-fold axis perpendicular to the plane. The core complex is an S-shaped dimer composed of two RCs, each encircled by 13 LH1 alpha/beta-heterodimers, and two PufXs. The LH1 assembly is an open ellipse with a topography-free gap of approximately 25 A. The two PufXs, one of each core, are located at the dimer center. Based on our data, we propose a model of the core complex, which provides explanation for the PufX-induced dimerization of the Rhodobacter core complex. The QB site is located facing a approximately 25-A wide gap within LH1, explaining the PufX-favored quinone passage in and out of the core complex.
authors.affiliation: Institut Curie, Unité Mixte de Recherche-CNRS 168 and Laboratoire de Recherche Correspondant-Commissariat à l'Energie Atomique 34V, 11 rue Pierre et Marie Curie, 75231 Paris 05, France. simon.scheuring@curie.fr
authors.forename: Simon
authors.initials: S
authors.lastname: Scheuring
authors.forename: Johan
authors.initials: J
authors.lastname: Busselez
authors.forename: Daniel
authors.initials: D
authors.lastname: Lévy
mesh_terms: D016227:Benzoquinones / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D046911:Macromolecular Substances / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D019897:Periplasm / Q000378:metabolism; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D020836:Protein Structure, Quaternary; D016992:Rhodobacter / Q000737:chemistry* / Q000145:classification / Q000166:cytology / Q000648:ultrastructure*
chemical_list: D016227:Benzoquinones; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; C004532:quinone