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Catalytic turnover triggers exchange of subunits of the magnesium chelatase AAA+ motor unit

Lundqvist, J.; Braumann, I.; Kurowska, M.; Muller, A. H. and Hansson, Mats LU (2013) In Journal of Biological Chemistry 288(33). p.24012-24019
Abstract
The ATP-dependent insertion of Mg(2+) into protoporphyrin IX is the first committed step in the chlorophyll biosynthetic pathway. The reaction is catalyzed by magnesium chelatase, which consists of three gene products: BchI, BchD, and BchH. The BchI and BchD subunits belong to the family of AAA+ proteins (ATPases associated with various cellular activities) and form a two-ring complex with six BchI subunits in one layer and six BchD subunits in the other layer. This BchID complex is a two-layered trimer of dimers with the ATP binding site located at the interface between two neighboring BchI subunits. ATP hydrolysis by the BchID motor unit fuels the insertion of Mg(2+) into the porphyrin by the BchH subunit. In the present study, we... (More)
The ATP-dependent insertion of Mg(2+) into protoporphyrin IX is the first committed step in the chlorophyll biosynthetic pathway. The reaction is catalyzed by magnesium chelatase, which consists of three gene products: BchI, BchD, and BchH. The BchI and BchD subunits belong to the family of AAA+ proteins (ATPases associated with various cellular activities) and form a two-ring complex with six BchI subunits in one layer and six BchD subunits in the other layer. This BchID complex is a two-layered trimer of dimers with the ATP binding site located at the interface between two neighboring BchI subunits. ATP hydrolysis by the BchID motor unit fuels the insertion of Mg(2+) into the porphyrin by the BchH subunit. In the present study, we explored mutations that were originally identified in semidominant barley (Hordeum vulgare L.) mutants. The resulting recombinant BchI proteins have marginal ATPase activity and cannot contribute to magnesium chelatase activity although they apparently form structurally correct complexes with BchD. Mixing experiments with modified and wild-type BchI in various combinations showed that an exchange of BchI subunits in magnesium chelatase occurs during the catalytic cycle, which indicates that dissociation of the complex may be part of the reaction mechanism related to product release. Mixing experiments also showed that more than three functional interfaces in the BchI ring structure are required for magnesium chelatase activity. (Less)
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Contribution to journal
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published
subject
keywords
Adenosine Triphosphatases/chemistry/metabolism, Adenosine Triphosphate/metabolism, *Biocatalysis, Chlorophyll/metabolism, Hordeum/*enzymology, Lyases/chemistry/*metabolism/ultrastructure, Molecular Motor Proteins/*metabolism, Mutation/genetics, Protein Multimerization, Protein Subunits/chemistry/*metabolism, Spectrophotometry, Aaa, ATPases, Biosynthesis, Chelatase, Chlorophyll Biosynthesis, Magnesium, Magnesium Chelatase, Plant Biochemistry, Porphyrin, Protoporphyrin
in
Journal of Biological Chemistry
volume
288
issue
33
pages
24012 - 24019
publisher
ASBMB
external identifiers
  • scopus:84882386220
ISSN
1083-351X
DOI
10.1074/jbc.M113.480012
language
English
LU publication?
no
id
5b6f0219-127d-41f6-813e-34bb6ab5af97 (old id 8001682)
alternative location
http://www.ncbi.nlm.nih.gov/pubmed/23836887
date added to LUP
2015-09-30 08:36:17
date last changed
2019-04-30 02:45:19
@article{5b6f0219-127d-41f6-813e-34bb6ab5af97,
  abstract     = {The ATP-dependent insertion of Mg(2+) into protoporphyrin IX is the first committed step in the chlorophyll biosynthetic pathway. The reaction is catalyzed by magnesium chelatase, which consists of three gene products: BchI, BchD, and BchH. The BchI and BchD subunits belong to the family of AAA+ proteins (ATPases associated with various cellular activities) and form a two-ring complex with six BchI subunits in one layer and six BchD subunits in the other layer. This BchID complex is a two-layered trimer of dimers with the ATP binding site located at the interface between two neighboring BchI subunits. ATP hydrolysis by the BchID motor unit fuels the insertion of Mg(2+) into the porphyrin by the BchH subunit. In the present study, we explored mutations that were originally identified in semidominant barley (Hordeum vulgare L.) mutants. The resulting recombinant BchI proteins have marginal ATPase activity and cannot contribute to magnesium chelatase activity although they apparently form structurally correct complexes with BchD. Mixing experiments with modified and wild-type BchI in various combinations showed that an exchange of BchI subunits in magnesium chelatase occurs during the catalytic cycle, which indicates that dissociation of the complex may be part of the reaction mechanism related to product release. Mixing experiments also showed that more than three functional interfaces in the BchI ring structure are required for magnesium chelatase activity.},
  author       = {Lundqvist, J. and Braumann, I. and Kurowska, M. and Muller, A. H. and Hansson, Mats},
  issn         = {1083-351X},
  keyword      = {Adenosine Triphosphatases/chemistry/metabolism,Adenosine Triphosphate/metabolism,*Biocatalysis,Chlorophyll/metabolism,Hordeum/*enzymology,Lyases/chemistry/*metabolism/ultrastructure,Molecular Motor Proteins/*metabolism,Mutation/genetics,Protein Multimerization,Protein Subunits/chemistry/*metabolism,Spectrophotometry,Aaa,ATPases,Biosynthesis,Chelatase,Chlorophyll Biosynthesis,Magnesium,Magnesium Chelatase,Plant Biochemistry,Porphyrin,Protoporphyrin},
  language     = {eng},
  number       = {33},
  pages        = {24012--24019},
  publisher    = {ASBMB},
  series       = {Journal of Biological Chemistry},
  title        = {Catalytic turnover triggers exchange of subunits of the magnesium chelatase AAA+ motor unit},
  url          = {http://dx.doi.org/10.1074/jbc.M113.480012},
  volume       = {288},
  year         = {2013},
}