The structural basis for the difference in absorbance spectra for the FMO antenna protein from various green sulfur bacteria

Photosynth Res. 2009 May;100(2):79-87. doi: 10.1007/s11120-009-9430-6. Epub 2009 May 13.


The absorbance spectrum of the Fenna-Matthews-Olson protein--a component of the antenna system of Green Sulfur Bacteria--is always one of two types, depending on the species of the source organism. The FMO from Prosthecochloris aestuarii 2K has a spectrum of type 1 while that from Chlorobaculum tepidum is of type 2. The previously reported crystal structures for these two proteins did not disclose any rationale that would explain their spectral differences. We have collected a 1.3 A X-ray diffraction dataset of the FMO from Prosthecochloris aestuarii 2K, which has allowed us to identify an additional Bacteriochlorophyll-a molecule with chemical attachments to both sides of the central magnesium atom. A new analysis of the previously published X-ray data for the Chlorobaculum tepidum FMO shows the presence of a Bacteriochlorophyll-a molecule in an equivalent location but with a chemical attachment from only one side. This difference in binding is shown to be predictive of the spectral type of the FMO.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism*
  • Chlorobi / chemistry*
  • Crystallography, X-Ray
  • Light-Harvesting Protein Complexes / chemistry*
  • Light-Harvesting Protein Complexes / metabolism*
  • Molecular Sequence Data
  • Protein Structure, Secondary
  • Sequence Alignment
  • Spectrum Analysis
  • Static Electricity
  • Structure-Activity Relationship


  • Bacterial Proteins
  • FMO bacteriochlorophyll protein, Bacteria
  • Light-Harvesting Protein Complexes