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Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway.

ABSTRACT: Three open reading frames in the Rhodobacter capsulatus photosynthesis gene cluster, designated F0, F108, and F1025, were disrupted by site-directed mutagenesis. Mutants bearing insertions in these reading frames were defective in converting protoporphyrin IX to magnesium-protoporphyrin monomethyl ester, protochlorophyllide to chlorophyllide a, and magnesium-protoporphyrin monomethyl ester to protochlorophyllide, respectively. These results demonstrate that the genes examined most likely encode enzyme subunits that catalyze steps common to plant and bacterial tetrapyrrole photopigment biosynthetic pathways. The open reading frames were found to be part of a large 11-kilobase operon that encodes numerous genes involved in early steps of the bacteriochlorophyll a biosynthetic pathway.

SUBMITTER: Yang ZM

PROVIDER: S-EPMC213156 | biostudies-other | 1990 Sep

REPOSITORIES: biostudies-other

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Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway.

Yang Z M ZM Bauer C E CE

Journal of bacteriology 19900901 9

Three open reading frames in the Rhodobacter capsulatus photosynthesis gene cluster, designated F0, F108, and F1025, were disrupted by site-directed mutagenesis. Mutants bearing insertions in these reading frames were defective in converting protoporphyrin IX to magnesium-protoporphyrin monomethyl ester, protochlorophyllide to chlorophyllide a, and magnesium-protoporphyrin monomethyl ester to protochlorophyllide, respectively. These results demonstrate that the genes examined most likely encode ...[more]

PMID: 2203738

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Project description:Bacterial microcompartments (BMCs) are large (?100-nm) protein shells that encapsulate enzymes, their substrates, and cofactors for the purposes of increasing metabolic reaction efficiency and protecting cells from toxic intermediates. The best-studied microcompartment is the carbon-fixing carboxysome that encapsulates ribulose-1,5-bisphosphate carboxylase and carbonic anhydrase. Other well-known BMCs include the Pdu and Eut BMCs, which metabolize 1,2-propanediol and ethanolamine, respectively, with vitamin B12-dependent diol dehydratase enzymes. Recent bioinformatic analyses identified a new prevalent type of BMC, hypothesized to utilize vitamin B12-independent glycyl radical enzymes to metabolize substrates. Here we use genetic and metabolic analyses to undertake in vivo characterization of the newly identified glycyl radical enzyme microcompartment 3 (GRM3) class of microcompartment clusters. Transcriptome sequencing analyses showed that the microcompartment gene cluster in the genome of the purple photosynthetic bacterium Rhodobacter capsulatus was expressed under dark anaerobic respiratory conditions in the presence of 1,2-propanediol. High-performance liquid chromatography and gas chromatography-mass spectrometry analyses showed that enzymes coded by this cluster metabolized 1,2-propanediol into propionaldehyde, propanol, and propionate. Surprisingly, the microcompartment pathway did not protect these cells from toxic propionaldehyde under the conditions used in this study, with buildup of this intermediate contributing to arrest of cell growth. We further show that expression of microcompartment genes is regulated by a two-component system located downstream of the microcompartment cluster.IMPORTANCE BMCs are protein shells that are designed to compartmentalize enzymatic reactions that require either sequestration of a substrate or the sequestration of toxic intermediates. Due to their ability to compartmentalize reactions, BMCs have also become attractive targets for bioengineering novel enzymatic reactions. Despite these useful features, little is known about the biochemistry of newly identified classes of BMCs. In this study, we have undertaken genetic and in vivo metabolic analyses of the newly identified GRM3 gene cluster.

Project description:Background In many works, the chemical composition of bacterially-produced elemental selenium nanoparticles (Se0-nanoparticles) was investigated using electron dispersive X-ray analysis. The results suggest that these particles should be associated with organic compounds. However, a complete analysis of their chemical composition is still missing. Aiming at identifying organic compounds associated with the Se0-nanoparticles produced by the purple phototrophic bacteria Rhodospirillum rubrum and Rhodobacter capsulatus (? group of the proteobacteria), we used MALDI-TOF spectrometry.Results This technic revealed that numerous signals obtained from particles produced by both species of bacteria were from metabolites of the photosynthetic system. Furthermore, not only bacteriochlorophyll a, bacteriopheophytin a, and bacteriopheophorbide a, which are known to accumulate in stationary phase cultures of these bacteria grown phototrophically in the absence of selenite, were identified. The particles were also associated with intermediary metabolites of the bacteriochlorophyll a biosynthesis pathway such as protoporphyrin IX, protoporphyrin IX monomethyl ester, bacteriochlorophyllide a and, most likely, Mg-protoporphyrin IX-monomethyl ester, as well as with oxidation products of the substrates of protochlorophyllide reductase and chlorin reductase.Conclusion Accumulation of intermediary metabolites of the bacteriochlorophyll biosynthesis pathway in these purple phototrophic bacteria was attributed to inhibition of oxygen-sensitive enzymes involved in this pathway. Consistent with this interpretation it has been reported that these bacteria reduce selenite intracellularly, that they contain high levels of glutathione and that the reduction of selenite with glutathione is a very fast reaction accompanied by the production of reactive oxygen species. As many enzymes involved in the biosynthesis of bacteriochlorophyll contain [Fe-S] clusters in their active site, which are known to be degraded in the presence of reactive oxygen species as well as in the presence of molecular oxygen, we concluded that the substrates of these enzymes accumulate in cells during selenite reduction.Association of metabolites of bacteriochlorophyll biosynthesis and degradation with the Se0-nanoparticles produced by Rhodospirillum rubrum and Rhodobacter capsulatus is proposed to result from coating of the nanoparticles with the intracytoplasmic membrane of these bacteria, where the photochemical apparatus is concentrated.

Dataset Information

Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway.

Publications

Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway.

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