title: Molecular architecture of photosynthetic membranes in Rhodobacter sphaeroides: the role of PufX.
abstract: The effects of the PufX polypeptide on membrane architecture were investigated by comparing the composition and structures of photosynthetic membranes from PufX+ and PufX- strains of Rhodobacter sphaeroides. We show that this single polypeptide profoundly affects membrane morphology, leading to highly elongated cells containing extended tubular membranes. Purified tubular membranes contain helical arrays composed solely of dimeric RC-LH1-PufX (RC, reaction centre; LH, light harvesting) complexes with apparently open LH1 rings. PufX- cells contain crystalline membranes with a pseudo-hexagonal packing of monomeric core complexes. Analysis of purified complexes by electron microscopy and atomic force microscopy shows that LH1 and PufX form a continuous ring of protein around each RC. A model of the tubular membrane is presented with PufX located adjacent to the stained region created by a vacant LH1beta. This arrangement, coupled with a flexible ring, would give the RC QB site transient access to the interstices in the lattice, which might be of functional importance. We discuss the implications of our data for the export of quinol from the RC, for eventual reduction of the cytochrome bc1 complex.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Krebs Institute for Biomolecular Research, Sheffield, UK.
authors.forename: C Alistair
authors.initials: CA
authors.lastname: Siebert
authors.forename: Pu
authors.initials: P
authors.lastname: Qian
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Fotiadis
authors.forename: Andreas
authors.initials: A
authors.lastname: Engel
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
authors.forename: Per A
authors.initials: PA
authors.lastname: Bullough
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure*; D002499:Centrifugation, Density Gradient; D003461:Crystallography; D019281:Dimerization; D014450:Electron Transport Complex III / Q000235:genetics / Q000378:metabolism; D005583:Fourier Analysis; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D009154:Mutation; D012242:Rhodobacter sphaeroides / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; C088749:PufX protein, Rhodobacter; D014450:Electron Transport Complex III