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Three semidominant barley mutants with single amino acid substitutions in the smallest magnesium chelatase subunit form defective AAA+ hexamers

Hansson, Andreas LU ; Willows, R D; Roberts, T H and Hansson, Mats LU (2002) In Proceedings of the National Academy of Sciences 99(21). p.13944-13949
Abstract
Many enzymes of the bacteriochlorophyll and chlorophyll biosynthesis pathways have been conserved throughout evolution, but the molecular mechanisms of the key steps remain unclear. The magnesium chelatase reaction is one of these steps, and it requires the proteins BchI, BchD, and BchH to catalyze the insertion of Mg2+ into protoporphyrin IX upon ATP hydrolysis. Structural analyses have shown that BchI forms hexamers and belongs to the ATPases associated with various cellular activities (AAA+) family of proteins. AAA+ proteins are Mg2+-dependent ATPases that normally form oligomeric ring structures in the presence of ATP. By using ATPase-deficient BchI subunits, we demonstrate that binding of ATP is sufficient to form BchI oligomers.... (More)
Many enzymes of the bacteriochlorophyll and chlorophyll biosynthesis pathways have been conserved throughout evolution, but the molecular mechanisms of the key steps remain unclear. The magnesium chelatase reaction is one of these steps, and it requires the proteins BchI, BchD, and BchH to catalyze the insertion of Mg2+ into protoporphyrin IX upon ATP hydrolysis. Structural analyses have shown that BchI forms hexamers and belongs to the ATPases associated with various cellular activities (AAA+) family of proteins. AAA+ proteins are Mg2+-dependent ATPases that normally form oligomeric ring structures in the presence of ATP. By using ATPase-deficient BchI subunits, we demonstrate that binding of ATP is sufficient to form BchI oligomers. Further, ATPase-deficient BchI proteins can form mixed oligomers with WT BchI. The formation of BchI oligomers is not sufficient for magnesium chelatase activity when combined with BchD and BchH. Combining WT BchI with ATPase-deficient BchI in an assay disrupts the chelatase reaction, but the presence of deficient BchI does not inhibit ATPase activity of the WT BchI. Thus, the ATPase of every WT segment of the hexamer is autonomous, but all segments of the hexamer must be capable of ATP hydrolysis for magnesium chelatase activity. We suggest that ATP hydrolysis of each BchI within the hexamer causes a conformational change of the hexamer as a whole. However, hexamers containing ATPase-deficient BchI are unable to perform this ATP-dependent conformational change, and the magnesium chelatase reaction is stalled in an early stage. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Proceedings of the National Academy of Sciences
volume
99
issue
21
pages
13944 - 13949
publisher
National Acad Sciences
external identifiers
  • wos:000178635700107
  • scopus:0037108759
ISSN
1091-6490
DOI
10.1073/pnas.212504499
language
English
LU publication?
yes
id
194689a1-b2a0-4f92-bb44-661345198df5 (old id 124791)
date added to LUP
2007-07-05 11:46:05
date last changed
2017-07-09 03:42:29
@article{194689a1-b2a0-4f92-bb44-661345198df5,
  abstract     = {Many enzymes of the bacteriochlorophyll and chlorophyll biosynthesis pathways have been conserved throughout evolution, but the molecular mechanisms of the key steps remain unclear. The magnesium chelatase reaction is one of these steps, and it requires the proteins BchI, BchD, and BchH to catalyze the insertion of Mg2+ into protoporphyrin IX upon ATP hydrolysis. Structural analyses have shown that BchI forms hexamers and belongs to the ATPases associated with various cellular activities (AAA+) family of proteins. AAA+ proteins are Mg2+-dependent ATPases that normally form oligomeric ring structures in the presence of ATP. By using ATPase-deficient BchI subunits, we demonstrate that binding of ATP is sufficient to form BchI oligomers. Further, ATPase-deficient BchI proteins can form mixed oligomers with WT BchI. The formation of BchI oligomers is not sufficient for magnesium chelatase activity when combined with BchD and BchH. Combining WT BchI with ATPase-deficient BchI in an assay disrupts the chelatase reaction, but the presence of deficient BchI does not inhibit ATPase activity of the WT BchI. Thus, the ATPase of every WT segment of the hexamer is autonomous, but all segments of the hexamer must be capable of ATP hydrolysis for magnesium chelatase activity. We suggest that ATP hydrolysis of each BchI within the hexamer causes a conformational change of the hexamer as a whole. However, hexamers containing ATPase-deficient BchI are unable to perform this ATP-dependent conformational change, and the magnesium chelatase reaction is stalled in an early stage.},
  author       = {Hansson, Andreas and Willows, R D and Roberts, T H and Hansson, Mats},
  issn         = {1091-6490},
  language     = {eng},
  number       = {21},
  pages        = {13944--13949},
  publisher    = {National Acad Sciences},
  series       = {Proceedings of the National Academy of Sciences},
  title        = {Three semidominant barley mutants with single amino acid substitutions in the smallest magnesium chelatase subunit form defective AAA+ hexamers},
  url          = {http://dx.doi.org/10.1073/pnas.212504499},
  volume       = {99},
  year         = {2002},
}