Archives of Microbiology

, Volume 188, Issue 6, pp 599–608 | Cite as

Rhodobacter capsulatus magnesium chelatase subunit BchH contains an oxygen sensitive iron–sulfur cluster

  • Nick SirijovskiEmail author
  • Fikret Mamedov
  • Ulf Olsson
  • Stenbjörn Styring
  • Mats Hansson
Original Paper


Magnesium chelatase is the first unique enzyme of the bacteriochlorophyll biosynthetic pathway. It consists of three subunits (BchI, BchD, and BchH). Amino acid sequence analysis of the Rhodobacter capsulatus BchH revealed a novel cysteine motif (393CX2CX3CX14C) that was found in only six other proteobacteria (CX2CX3CX11–14C). The cysteine motif is likely to coordinate an unprecedented [Fe–S] cluster. Purified BchH demonstrated absorbance in the 460 nm region. This absorbance was abolished in BchH proteins with alanine substitutions at positions Cys396 and Cys414. These modified proteins were also EPR silent. In contrast, wild type BchH protein in the reduced state showed EPR signals resembling those of a [4Fe–4S] cluster with rhombic symmetry and g values at 1.90, 1.93, and 2.09, superimposed with a [3Fe–4S] cluster centered at g = 2.02. The [3Fe–4S] signal was observed independently of the [4Fe–4S] signal under oxidizing conditions. Mg-chelatase activity assays showed that the cluster is not catalytic. We suggest that the [4Fe–4S] and [3Fe–4S] signals originate from a single coordination site on the monomeric BchH protein and that the [4Fe–4S] cluster is sensitive to oxidation. It is speculated that the cluster participates in the switching between aerobic and anaerobic life of the proteobacteria.


Bacteriochlorophyll chlH Chlorophyll Tetrapyrrole Xantha-f Enzyme: Magnesium chelatase EC 



ATPase associated with various cellular activities






Isopropyl β-d-1-thiogalactopyranoside


Magnesium protoporphyrin monomethylester


Phenazine methosulfate


Phenylmethylsulfonyl fluoride


Purple nonsulfur bacteria



We thank Dr. Cecilia Hagerhäll for fruitful discussions. NS greatly acknowledges a fellowship from the Sven and Lilly Lawski Foundation. This work was supported by the Swedish Research Council (MH, FM, and SS), the Swedish National Energy Administration, DESS and the Knut and Alice Wallenberg Foundation (FM and SS).


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Nick Sirijovski
    • 1
    Email author
  • Fikret Mamedov
    • 2
  • Ulf Olsson
    • 1
  • Stenbjörn Styring
    • 2
  • Mats Hansson
    • 1
  1. 1.Department of Biochemistry, Center for Molecular Protein ScienceLund UniversityLundSweden
  2. 2.Department of Photochemistry and Molecular ScienceUppsala UniversityUppsalaSweden

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