ATP-induced conformational dynamics in the AAA+ motor unit of magnesium chelatase.
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.
Lundqvist
Joakim
J
Department of Molecular Biophysics, Centre for Molecular Protein Science, Lund University, Lund, Sweden. joakim@crc.dk
Elmlund
Hans
H
Wulff
Ragna Peterson
RP
Berglund
Lisa
L
Elmlund
Dominika
D
Emanuelsson
Cecilia
C
Hebert
Hans
H
Willows
Robert D
RD
Hansson
Mats
M
Lindahl
Martin
M
Al-Karadaghi
Salam
S
D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D020285:Cryoelectron Microscopy; D005798:Genes, Bacterial; D008190:Lyases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016354:Rhodobacter capsulatus / Q000378:metabolism
D001426:Bacterial Proteins; D000255:Adenosine Triphosphate; D008190:Lyases; C086788:magnesium chelatase