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Structural model and excitonic properties of the dimeric RC–LH1–PufX complex from Rhodobacter sphaeroides

2009; Elsevier BV; Volume: 357; Issue: 1-3 Linguagem: Inglês

10.1016/j.chemphys.2009.01.003

1873-4421

Melih Şener, Jen Hsin, Leonardo G. Trabuco, Elizabeth Villa, Qian Pu, C. Neil Hunter, Klaus Schulten,

Spectroscopy and Quantum Chemical Studies

The light-harvesting apparatus of the purple bacterial photosynthetic unit consists of a pool of peripheral light-harvesting complexes that transfer excitation energy to a reaction center (RC) via the surrounding pigment-protein complex LH1. Recent electron microscopy and atomic force microscopy studies have revealed that RC-LH1 units of Rhodobacter sphaeroides form membrane-bending dimeric complexes together with the polypeptide PufX. We present a structural model for these RC-LH1-PufX dimeric complexes constructed using the molecular dynamics flexible fitting method based on an EM density map. The arrangement of the LH1 BChls displays a distortion near the proposed location of the PufX polypeptide. The resulting atomic model for BChl arrays is used to compute the excitonic properties of the dimeric RC-LH1 complex. A comparison is presented between the structural and excitonic features of the S-shaped dimeric BChl array of Rhodobacter sphaeroides and the circular BChl arrangement found in other purple bacteria.