View the Current Issue

Article

  • The EMBO Journal (2004) 23, 690 - 700
  • doi:10.1038/sj.emboj.7600092

Published online: 5 February 2004

Molecular architecture of photosynthetic membranes in Rhodobacter sphaeroides: the role of PufX

C Alistair Siebert1, Pu Qian1, Dimitrios Fotiadis2, Andreas Engel2, C Neil Hunter1 and Per A Bullough1

  1. Department of Molecular Biology and Biotechnology, University of Sheffield, Krebs Institute for Biomolecular Research, Sheffield, UK
  2. University of Basel, Biozentrum, ME Müller Institute for Structural Biology, Basel, Switzerland

Correspondence to:

Per A Bullough, Department of Molecular Biology and Biotechnology, University of Sheffield, Krebs Institute for Biomolecular Research, Firth Court, Western Bank, Sheffield S10 2TN, UK. Tel.: +44 114 222 4245; Fax: +44 114 272 8697; E-mail: p.bullough@sheffield.ac.uk

Received 27 October 2003; Accepted 5 January 2004

The effects of the PufX polypeptide on membrane architecture were investigated by comparing the composition and structures of photosynthetic membranes from PufX+ and PufX- strains of Rhodobacter sphaeroides. We show that this single polypeptide profoundly affects membrane morphology, leading to highly elongated cells containing extended tubular membranes. Purified tubular membranes contain helical arrays composed solely of dimeric RC–LH1–PufX (RC, reaction centre; LH, light harvesting) complexes with apparently open LH1 rings. PufX- cells contain crystalline membranes with a pseudo-hexagonal packing of monomeric core complexes. Analysis of purified complexes by electron microscopy and atomic force microscopy shows that LH1 and PufX form a continuous ring of protein around each RC. A model of the tubular membrane is presented with PufX located adjacent to the stained region created by a vacant LH1beta. This arrangement, coupled with a flexible ring, would give the RC QB site transient access to the interstices in the lattice, which might be of functional importance. We discuss the implications of our data for the export of quinol from the RC, for eventual reduction of the cytochrome bc1 complex.

  • Keywords:

    • 2D crystals,
    • cytochrome bc1 complex,
    • light harvesting complex,
    • reaction centre,
    • photosynthesis