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AKB: Biologische Physik

AKB 40: Poster Session II

AKB 40.53: Poster

Mittwoch, 29. März 2006, 16:30–19:30, P3

Form follows function: how PufX–induced dimerization improves the efficiency of the light harvesting complexes of Rb. sphaeroides — •Tihamer Geyer — Zentrum für Bioinformatik, Universität des Saarlandes, D-66041 Saarbrücken

Lately there has been renewed interest in the "mystery" protein PufX, which occurs in the purple bacteria Rb. sphaeroides and Rb. capsulatus. It is responsible there for a dimerization of the light harvesting complexes of type I (LH1). It’s key function seems to be to open the LH1 rings for eased diffusion of the quinones to the enclosed reaction centers (RC).

We show that the symmetry breaking induced by PufX also has an important effect on the main purpose of the LH1s, which is to help the RCs to absorb light. For this we extend a simple dipole model of the bacteriochlorophyll (Bchl) arrays of the LH1 and the RC [Hu etal, J. Phys. Chem 101 (1997) 3854] to calculate the absoprtion properties of the PufX induced LH1 dimers and their coupling to the special pair Bchls of the RCs. Comparison with the closed monomeric LH1/RC unit shows that the dimer has the same photosynthetically effective absorption cross section per monomer though it contains less Bchls. Additionally, the dimeric setup reduces the statistical fluctuations in the photon rate for the two RCs, thus further increasing the efficiency of photosynthesis.