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Molecular Basis for Semidominance of Missense Mutations in the XANTHA-H (42-kDa) Subunit of Magnesium Chelatase

Hansson, Andreas LU ; Gamini Kannangara, C; von Wettstein, Diter and Hansson, Mats LU (1999) In Proceedings of the National Academy of Sciences 96(4). p.1744-1749
Abstract
During biosynthesis of bacteriochlorophyll or chlorophyll, three protein subunits of 140, 70, and 42 kDa interact to insert Mg2+ into protoporphyrin IX. The semi-dominant Chlorina-125,-157, and -161 mutants in barley are deficient in this step and accumulate protoporphyrin IX after feeding on 5-aminolevulinate. Chlorina-125,-157, and -161 are allelic to the recessive xantha-h mutants and contain G559A, G806A, and C271T mutations, respectively. These mutations cause single amino acid substitutions in residues that are conserved in all known primary structures of the 42-kDa subunit. In vitro complementation and reconstitution of Mg-chelatase activity show that the 42-kDa subunits are defective in the semidominant Chlorina mutants. A mutated... (More)
During biosynthesis of bacteriochlorophyll or chlorophyll, three protein subunits of 140, 70, and 42 kDa interact to insert Mg2+ into protoporphyrin IX. The semi-dominant Chlorina-125,-157, and -161 mutants in barley are deficient in this step and accumulate protoporphyrin IX after feeding on 5-aminolevulinate. Chlorina-125,-157, and -161 are allelic to the recessive xantha-h mutants and contain G559A, G806A, and C271T mutations, respectively. These mutations cause single amino acid substitutions in residues that are conserved in all known primary structures of the 42-kDa subunit. In vitro complementation and reconstitution of Mg-chelatase activity show that the 42-kDa subunits are defective in the semidominant Chlorina mutants. A mutated protein is maintained in the Chlorina plastids, unlike in the xantha-h plastids. Heterozygous Chlorina seedlings have 25-50% of the Mg-chelatase activity of wild-type seedlings. Codominant expression of active and inactive 42-kDa subunits in heterozygous Chlorina seedlings is likely to produce two types of heterodimers between the strongly interacting 42-kDa and 70-kDa subunits. Reduced Mg-chelatase activity is explained by the capacity of heterodimers consisting of mutated 42-kDa and wild-type 70-kDa protein to the 140-kDa subunit. The 42-kDa subunit is similar to chaperones that refold denatured polypeptides with respect to its ATP-to-ADP exchange activity and its ability to generate ATPase activity with the 70-kDa subunit. We hypothesize that the association of the 42-kDa subunit with the 70-kDa subunit allows them to form a specific complex with the 140-kDa subunit and that this complex inserts Mg2+ into protoporphyrin IX. (Less)
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author
organization
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type
Contribution to journal
publication status
published
subject
keywords
Plant Biology
in
Proceedings of the National Academy of Sciences
volume
96
issue
4
pages
1744 - 1749
publisher
National Acad Sciences
external identifiers
  • scopus:0033573997
ISSN
1091-6490
language
English
LU publication?
yes
id
6d18db3d-8fe7-49f5-8f1b-9e064345656f (old id 125309)
alternative location
http://www.pnas.org/cgi/content/abstract/96/4/1744
date added to LUP
2007-07-05 11:54:58
date last changed
2017-04-30 08:35:52
@article{6d18db3d-8fe7-49f5-8f1b-9e064345656f,
  abstract     = {During biosynthesis of bacteriochlorophyll or chlorophyll, three protein subunits of 140, 70, and 42 kDa interact to insert Mg2+ into protoporphyrin IX. The semi-dominant Chlorina-125,-157, and -161 mutants in barley are deficient in this step and accumulate protoporphyrin IX after feeding on 5-aminolevulinate. Chlorina-125,-157, and -161 are allelic to the recessive xantha-h mutants and contain G559A, G806A, and C271T mutations, respectively. These mutations cause single amino acid substitutions in residues that are conserved in all known primary structures of the 42-kDa subunit. In vitro complementation and reconstitution of Mg-chelatase activity show that the 42-kDa subunits are defective in the semidominant Chlorina mutants. A mutated protein is maintained in the Chlorina plastids, unlike in the xantha-h plastids. Heterozygous Chlorina seedlings have 25-50% of the Mg-chelatase activity of wild-type seedlings. Codominant expression of active and inactive 42-kDa subunits in heterozygous Chlorina seedlings is likely to produce two types of heterodimers between the strongly interacting 42-kDa and 70-kDa subunits. Reduced Mg-chelatase activity is explained by the capacity of heterodimers consisting of mutated 42-kDa and wild-type 70-kDa protein to the 140-kDa subunit. The 42-kDa subunit is similar to chaperones that refold denatured polypeptides with respect to its ATP-to-ADP exchange activity and its ability to generate ATPase activity with the 70-kDa subunit. We hypothesize that the association of the 42-kDa subunit with the 70-kDa subunit allows them to form a specific complex with the 140-kDa subunit and that this complex inserts Mg2+ into protoporphyrin IX.},
  author       = {Hansson, Andreas and Gamini Kannangara, C and von Wettstein, Diter and Hansson, Mats},
  issn         = {1091-6490},
  keyword      = {Plant Biology},
  language     = {eng},
  number       = {4},
  pages        = {1744--1749},
  publisher    = {National Acad Sciences},
  series       = {Proceedings of the National Academy of Sciences},
  title        = {Molecular Basis for Semidominance of Missense Mutations in the XANTHA-H (42-kDa) Subunit of Magnesium Chelatase},
  volume       = {96},
  year         = {1999},
}