Atomic-level structural and functional model of a bacterial photosynthetic membrane vesicle.
The photosynthetic unit (PSU) of purple photosynthetic bacteria consists of a network of bacteriochlorophyll-protein complexes that absorb solar energy for eventual conversion to ATP. Because of its remarkable simplicity, the PSU can serve as a prototype for studies of cellular organelles. In the purple bacterium Rhodobacter sphaeroides the PSU forms spherical invaginations of the inner membrane, approximately 70 nm in diameter, composed mostly of light-harvesting complexes, LH1 and LH2, and reaction centers (RCs). Atomic force microscopy studies of the intracytoplasmic membrane have revealed the overall spatial organization of the PSU. In the present study these atomic force microscopy data were used to construct three-dimensional models of an entire membrane vesicle at the atomic level by using the known structure of the LH2 complex and a structural model of the dimeric RC-LH1 complex. Two models depict vesicles consisting of 9 or 18 dimeric RC-LH1 complexes and 144 or 101 LH2 complexes, representing a total of 3,879 or 4,464 bacteriochlorophylls, respectively. The in silico reconstructions permit a detailed description of light absorption and electronic excitation migration, including computation of a 50-ps excitation lifetime and a 95% quantum efficiency for one of the model membranes, and demonstration of excitation sharing within the closely packed RC-LH1 dimer arrays.
Sener
Melih K
MK
Beckman Institute and Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. melih@ks.uiuc.edu
Olsen
John D
JD
Hunter
C Neil
CN
Schulten
Klaus
K
D000255:Adenosine Triphosphate / Q000378:metabolism; D020130:Bacterial Chromatophores / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D019281:Dimerization; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D018625:Microscopy, Atomic Force / Q000379:methods; D008958:Models, Molecular; D010788:Photosynthesis; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000378:metabolism
D001426:Bacterial Proteins; D008565:Membrane Proteins; D000255:Adenosine Triphosphate; D014450:Electron Transport Complex III