In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 96, No. 4 ( 1999-02-16), p. 1744-1749
Abstract:
During biosynthesis of bacteriochlorophyll or chlorophyll, three
protein subunits of 140, 70, and 42 kDa interact to insert Mg 2+ into protoporphyrin IX. The semidominant 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 bind 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 Mg 2+ into protoporphyrin IX.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.96.4.1744
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
1999
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
Bookmarklink