Structural role of PufX in the dimerization of the photosynthetic core complex of Rhodobacter sphaeroides.
Monomeric and dimeric PufX-containing core complexes have been purified from membranes of wild-type Rhodobacter sphaeroides. Reconstitution of both samples by detergent removal in the presence of lipids leads to the formation of two-dimensional crystals constituted of dimeric core complexes. Two-dimensional crystals were further analyzed by cryoelectron microscopy and atomic force microscopy. A projection map at 26-A resolution reveals that core complexes assemble in an "S"-shaped dimeric complex. Each core complex is composed of one reaction center, 12 light-harvesting 1 alpha/beta-heterodimers, and one PufX protein. The light-harvesting 1 assemblies are open with a gap of density of approximately 30-A width and surround oriented reaction centers. A maximum density is found at the dimer junction. Based on the projection map, a model is proposed, in which the two PufX proteins are located at the dimer junction, consistent with the finding of dimerization of monomeric core complexes upon reconstitution. This localization of PufX in the core complex implies that PufX is the structural key for the dimer complex formation rather than a channel-forming protein for the exchange of ubiquinone/ubiquinol between the reaction center and the cytochrome bc1 complex.
Scheuring
Simon
S
Institut Curie, UMR-CNRS 168 and LRC-CEA 34V, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05, France.
Francia
Francesco
F
Busselez
Johan
J
Melandri
Bruno Andrea
BA
Rigaud
Jean-Louis
JL
Lévy
Daniel
D
D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D020285:Cryoelectron Microscopy; D003902:Detergents / Q000494:pharmacology; D019281:Dimerization; D014450:Electron Transport Complex III / Q000737:chemistry; D007091:Image Processing, Computer-Assisted; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000502:physiology*; D008055:Lipids / Q000737:chemistry; D018625:Microscopy, Atomic Force; D010788:Photosynthesis; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D014451:Ubiquinone / Q000737:chemistry
D001426:Bacterial Proteins; D003902:Detergents; D045342:Light-Harvesting Protein Complexes; D008055:Lipids; C088749:PufX protein, Rhodobacter; D014451:Ubiquinone; D014450:Electron Transport Complex III