Physical mapping and functional assignment of the geranylgeranyl-bacteriochlorophyll reductase gene, bchP, of Rhodobacter sphaeroides.
The bacteriochlorophyll of the purple photosynthetic bacterium Rhodobacter sphaeroides is esterified with phytol. The presence of this alcohol moiety is essential for the correct assembly of the photosynthetic apparatus. Despite this, and the fact that R. sphaeroides is widely used for the study of structure-function relationships in photosynthesis, the molecular genetics of the steps in which the alcohol is added and modified have not previously been investigated in this organism. Sequencing near the center of the photosynthesis gene cluster has now revealed the existence of an open reading frame encoding a putative 394-amino-acid polypeptide displaying strong homology with the products of a number of genes from other photosynthetic organisms, each proposed to be responsible for the reduction of the alcohol moiety of (bacterio)chlorophyll to phytol. An R. sphaeroides transposon mutant in this gene, bchP, possessed a structurally modified photosystem assembled with bacteriochlorophyll esterified with geranylgeraniol, rather than with phytol, implying that the product of this gene was geranylgeranyl-bacteriochlorophyll reductase. This identification was confirmed by the performance of in vitro assays using heterologously expressed protein, providing the first direct demonstration of the activity of a bchP gene product.
Addlesee
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Robert Hill Institute for Photosynthesis and Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom. h.a.addlesee@sheffield.ac.uk
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D000595:Amino Acid Sequence; D001483:Base Sequence; D019729:Carbon-Oxygen Ligases; D002851:Chromatography, High Pressure Liquid; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D008961:Models, Structural; D008969:Molecular Sequence Data; D005810:Multigene Family; D016296:Mutagenesis; D016366:Open Reading Frames; D010088:Oxidoreductases / Q000235:genetics*; D020161:Physical Chromosome Mapping; D012242:Rhodobacter sphaeroides / Q000201:enzymology* / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
D004251:DNA Transposable Elements; D010088:Oxidoreductases; C402429:geranylgeranyl-bacteriochlorophyll reductase; D019729:Carbon-Oxygen Ligases; C105512:bacteriochlorophyll a synthase