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29 March 2024
 
  » arxiv » q-bio/0605023

 Article overview


Form follows function: how PufX-induced dimerization improves the efficiency of the light harvesting complexes from Rb. sphaeroides
Tihamer Geyer ;
Date 16 May 2006
Subject Quantitative Methods
AbstractSome purple bacteria, as, e.g., Rhodobacter sphaeroides, express an additional small protein PufX together with their photosynthetic reaction center (RC). When PufX is present, the light harvesting complexes of type 1 (LH1), which otherwise form closed rings around the RCs, occur in an open, Z-shaped dimeric configuration. According to recent speculations the purpose of PufX is to open the LH1 ring to facilitate diffusion of the membrane bound electron carrier ubiquinone to and from the reaction center.
Here we start from a different hypothesis, proposing that the PufX induced modifications to the LH1 are related to their function of being the antennae of the RCs. To check this assumption a simple dipole model [Hu et al, J. Phys. Chem. B 101 3854 (1997)] is used to calculate the absorption properties of the PufX induced LH1 dimers and their coupling to the special pair bacteriochlorophylls (Bchl) of the enclosed RCs. Comparison with the closed monomeric LH1/RC unit shows that for optimal orientation of the RCs the dimer has an even higher photosynthetic absorption cross section, though it contains less Bchls than two monomers. The orientation of the RCs, which gives the maximal photosynthetic efficiency, agrees very well with the reconstruction from recent EM images.
The absorption properties of monomeric partial rings then show that even more efficient configurations could be built with less than a three quarter LH1 ring. From our findings we hypothesize that PufX is necessary to maintain the structural stability of the LH1/RC complex in the more efficient open configuration.
Source arXiv, q-bio/0605023
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