Dataset Information

Roles of RubisCO and the RubisCO-like protein in 5-methylthioadenosine metabolism in the Nonsulfur purple bacterium Rhodospirillum rubrum.

ABSTRACT: Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) catalyzes the assimilation of atmospheric CO(2) into organic matter and is thus central to the existence of life on earth. The beginning of the 2000s was marked by the discovery of a new family of proteins, the RubisCO-like proteins (RLPs), which are structural homologs of RubisCO. RLPs are unable to catalyze CO(2) fixation. The RLPs from Chlorobaculum tepidum, Bacillus subtilis, Geobacillus kaustophilus, and Microcystis aeruginosa have been shown to participate in sulfur metabolism. Whereas the precise function of C. tepidum RLP is unknown, the B. subtilis, G. kaustophilus, and M. aeruginosa RLPs function as tautomerases/enolases in a methionine salvage pathway (MSP). Here, we show that the form II RubisCO enzyme from the nonsulfur purple bacterium Rhodospirillum rubrum is also able to function as an enolase in vivo as part of an MSP, but only under anaerobic conditions. However, unlike B. subtilis RLP, R. rubrum RLP does not catalyze the enolization of 2,3-diketo-5-methylthiopentyl-1-phosphate. Instead, under aerobic growth conditions, R. rubrum RLP employs another intermediate of the MSP, 5-methylthioribulose-1-phosphate, as a substrate, resulting in the formation of different products. To further determine the interrelationship between RubisCOs and RLPs (and the potential integration of cellular carbon and sulfur metabolism), the functional roles of both RubisCO and RLP have been examined in vivo via the use of specific knockout strains and complementation studies of R. rubrum. The presence of functional, yet separate, MSPs in R. rubrum under both aerobic (chemoheterotrophic) and anaerobic (photoheterotrophic) growth conditions has not been observed previously in any organism. Moreover, the aerobic and anaerobic sulfur salvage pathways appear to be differentially controlled, with novel and previously undescribed steps apparent for sulfur salvage in this organism.

SUBMITTER: Singh J

PROVIDER: S-EPMC2820871 | biostudies-other | 2010 Mar

REPOSITORIES: biostudies-other

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Publications

Roles of RubisCO and the RubisCO-like protein in 5-methylthioadenosine metabolism in the Nonsulfur purple bacterium Rhodospirillum rubrum.

Singh Jaya J Tabita F Robert FR

Journal of bacteriology 20091228 5

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) catalyzes the assimilation of atmospheric CO(2) into organic matter and is thus central to the existence of life on earth. The beginning of the 2000s was marked by the discovery of a new family of proteins, the RubisCO-like proteins (RLPs), which are structural homologs of RubisCO. RLPs are unable to catalyze CO(2) fixation. The RLPs from Chlorobaculum tepidum, Bacillus subtilis, Geobacillus kaustophilus, and Microcystis aeruginosa have b ...[more]

PMID: 20038587

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Project description:Rhodospirillum rubrum possesses a novel oxygen-independent, aerobic methionine salvage pathway (MSP) for recycling methionine from 5-methylthioadenosine (MTA), the MTA-isoprenoid shunt. This organism can also metabolize MTA as a sulfur source under anaerobic conditions, suggesting that the MTA-isoprenoid shunt may also function anaerobically as well. In this study, deep proteomics profiling, directed metabolite analysis, and reverse transcriptase quantitative PCR (RT-qPCR) revealed metabolic changes in response to anaerobic growth on MTA versus sulfate as sole sulfur source. The abundance of protein levels associated with methionine transport, cell motility, and chemotaxis increased in the presence of MTA over that in the presence of sulfate. Purine salvage from MTA resulted primarily in hypoxanthine accumulation and a decrease in protein levels involved in GMP-to-AMP conversion to balance purine pools. Acyl coenzyme A (acyl-CoA) metabolic protein levels for lipid metabolism were lower in abundance, whereas poly-β-hydroxybutyrate synthesis and storage were increased nearly 10-fold. The known R. rubrum aerobic MSP was also shown to be upregulated, to function anaerobically, and to recycle MTA. This suggested that other organisms with gene homologues for the MTA-isoprenoid shunt may also possess a functioning anaerobic MSP. In support of our previous findings that ribulose-1,5-carboxylase/oxygenase (RubisCO) is required for an apparently purely anaerobic MSP, RubisCO transcript and protein levels both increased in abundance by over 10-fold in cells grown anaerobically on MTA over those in cells grown on sulfate, resulting in increased intracellular RubisCO activity. These results reveal for the first time global metabolic responses as a consequence of anaerobic MTA metabolism compared to using sulfate as the sulfur source. In nearly all organisms, sulfur-containing byproducts result from many metabolic reactions. Unless these compounds are further metabolized, valuable organic sulfur is lost and can become limiting. To regenerate the sulfur-containing amino acid methionine, organisms typically employ one of several variations of a "universal" methionine salvage pathway (MSP). A common aspect of the universal MSP is a final oxygenation step. This work establishes that the metabolically versatile bacterium Rhodospirillum rubrum employs a novel MSP that does not require oxygen under either aerobic or anaerobic conditions. There is also a separate, dedicated anaerobic MTA metabolic route in R. rubrum This work reveals global changes in cellular metabolism in response to anaerobic MTA metabolism compared to using sulfate as a sulfur source. We found that cell mobility and transport were enhanced, along with lipid, nucleotide, and carbohydrate metabolism, when cells were grown in the presence of MTA.

Dataset Information

Roles of RubisCO and the RubisCO-like protein in 5-methylthioadenosine metabolism in the Nonsulfur purple bacterium Rhodospirillum rubrum.

Publications

Roles of RubisCO and the RubisCO-like protein in 5-methylthioadenosine metabolism in the Nonsulfur purple bacterium Rhodospirillum rubrum.

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