Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry?

J Mol Biol. 1998 Oct 2;282(4):819-31. doi: 10.1006/jmbi.1998.1975.

Abstract

The basic photosynthetic unit containing the reaction centre and the light-harvesting I complex (RC-LHI) of the purple non-sulphur bacterium Rhodospirillum rubrum was purified and reconstituted into two-dimensional (2D) membrane crystals. Transmission electron microscopy using conventional techniques and cryoelectron microscopy of the purified single particles and of 2D crystals yielded a projection of the RC-LHI complex at a resolution of at least 1.6 nm. In this projection the LHI ring appears to have a square symmetry and packs in a square crystal lattice. The square geometry of the LHI ring was observed also in images of single isolated particles of the RC-LHI complex. However, although the LHI units are packed identically within the crystal lattice, a new rotational analysis developed here showed that the reaction centres take up one of four possible orientations within the ring. This fourfold disorder supports our interpretation of a square ring symmetry and suggests that a hitherto undetected component may be present within the photosynthetic unit.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Chromatophores / chemistry
  • Bacterial Proteins*
  • Cryoelectron Microscopy
  • Crystallization
  • Hydrogen-Ion Concentration
  • Light-Harvesting Protein Complexes*
  • Microdialysis
  • Microscopy, Electron
  • Molecular Weight
  • Phospholipid Ethers
  • Photosynthetic Reaction Center Complex Proteins / chemistry
  • Photosynthetic Reaction Center Complex Proteins / isolation & purification
  • Photosynthetic Reaction Center Complex Proteins / ultrastructure*
  • Protein Conformation
  • Rhodospirillum rubrum / chemistry*
  • Solubility
  • Spectrum Analysis

Substances

  • 1,2-dihexadecyl-sn-glycero-3-phosphocholine
  • Bacterial Proteins
  • Light-Harvesting Protein Complexes
  • Phospholipid Ethers
  • Photosynthetic Reaction Center Complex Proteins
  • light-harvesting complex 1, Rhodospirillum