Magnesium-protoporphyrin chelatase of Rhodobacter sphaeroides: reconstitution of activity by combining the products of the bchH, -I, and -D genes expressed in Escherichia coli.
Magnesium-protoporphyrin chelatase lies at the branch point of the heme and (bacterio)chlorophyll biosynthetic pathways. In this work, the photosynthetic bacterium Rhodobacter sphaeroides has been used as a model system for the study of this reaction. The bchH and the bchI and -D genes from R. sphaeroides were expressed in Escherichia coli. When cell-free extracts from strains expressing BchH, BchI, and BchD were combined, the mixture was able to catalyze the insertion of Mg into protoporphyrin IX in an ATP-dependent manner. This was possible only when all three genes were expressed. The bchH, -I, and -D gene products are therefore assigned to the Mg chelatase step in bacteriochlorophyll biosynthesis. The mechanism of the Mg chelation reaction and the implications for chlorophyll biosynthesis in plants are discussed.
Gibson
L C
LC
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, United Kingdom.
Willows
R D
RD
Kannangara
C G
CG
von Wettstein
D
D
Hunter
C N
CN
D000255:Adenosine Triphosphate / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004926:Escherichia coli; D015870:Gene Expression; D005798:Genes, Bacterial; D007700:Kinetics; D008190:Lyases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010788:Photosynthesis / Q000235:genetics; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000201:enzymology* / Q000235:genetics; D013053:Spectrophotometry
D017931:DNA Primers; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D008190:Lyases; C086788:magnesium chelatase