Melih K. Sener, John D. Olsen, C. Neil Hunter, and Klaus Schulten.
Atomic level structural and functional model of a bacterial
photosynthetic membrane vesicle.
Proceedings of the National Academy of Sciences, USA,
104:15723-15728, 2007.
(PMC: 2000399)
SENE2007
The photosynthetic unit (PSU) of purple photosynthetic bacteria consists of a network
of bacteriochlorophyll (BChl) protein complexes that absorb solar energy for eventual conversion to ATP. Due to its remarkable simplicity, the PSU can serve as a prototype for studies of cellular organelles. In the purple bacterium Rhodobacter (Rb.) sphaeroides the PSU forms spherical invaginations of the inner membrane, approximately 70nm in diameter, composed mostly of light harvesting complexes, LH1 and LH2, as well as reaction centers (RCs). Atomic force microscopy (AFM) studies of the intracytoplasmic membrane have revealed the overall spatial organization of the PSU. In the present study these AFM data were used to construct three-dimensional models of an entire membrane vesicle at the atomic level, 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 3879 or 4464 Bchls, 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.
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