ATP-induced conformational dynamics in the AAA+ motor unit of magnesium chelatase

Structure. 2010 Mar 10;18(3):354-65. doi: 10.1016/j.str.2010.01.001.


Mg-chelatase catalyzes the first committed step of the chlorophyll biosynthetic pathway, the ATP-dependent insertion of Mg(2+) into protoporphyrin IX (PPIX). Here we report the reconstruction using single-particle cryo-electron microscopy of the complex between subunits BchD and BchI of Rhodobacter capsulatus Mg-chelatase in the presence of ADP, the nonhydrolyzable ATP analog AMPPNP, and ATP at 7.5 A, 14 A, and 13 A resolution, respectively. We show that the two AAA+ modules of the subunits form a unique complex of 3 dimers related by a three-fold axis. The reconstructions demonstrate substantial differences between the conformations of the complex in the presence of ATP and ADP, and suggest that the C-terminal integrin-I domains of the BchD subunits play a central role in transmitting conformational changes of BchI to BchD. Based on these data a model for the function of magnesium chelatase is proposed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / chemistry*
  • Adenosine Triphosphate / metabolism
  • Amino Acid Sequence
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Cryoelectron Microscopy
  • Genes, Bacterial
  • Lyases / chemistry*
  • Lyases / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Conformation
  • Rhodobacter capsulatus / metabolism


  • Bacterial Proteins
  • Adenosine Triphosphate
  • Lyases
  • magnesium chelatase