Aspartate transport in Rhizobium meliloti

Watson, R. J.; Rastogi, Vipin K.; Chan, Yiu-Kwok

doi:10.1099/00221287-139-6-1315

Cited by 22 publications

(16 citation statements)

References 30 publications

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“…This has been attributed to DctA's ability to transport dicarboxylic acids, which are thought to be a major carbon and energy source for nitrogen-fixing bacteria. Previous work showed that the dicarboxylic acids succinate, malate, fumarate, and aspartate are DctA substrates (5,6,19). DctA is the major, if not the only, dicarboxylate transporter in S. meliloti, in contrast to E. coli, which has several Dct systems.…”

Section: Discussionmentioning

confidence: 97%

“…In contrast to orotate, which is a good substrate but not an inducer of DctA, maleate and asparagine were recognized as inducers of DctA but not as inhibitors of DctA transport. In this they resemble aspartate, which had been recognized as the strongest inducer among compounds previously tested but is not a very good substrate for transport, with a K m about 600-fold less than those of the TCA cycle dicarboxylic acids succinate, malate, and fumarate (19). Orotate can be considered a representative compound that appears to interact with DctA but not with DctB.…”

Section: Discussionmentioning

confidence: 99%

“…The apparent K m and V max for orotate transport were 1.7 mM and 163 nmol (min ⅐ mg of protein) Ϫ1 , respectively. It has been reported that the apparent K m for succinate transport is 15 M, while that for aspartate transport is 10 mM (19). Thus, the affinity of the Dct system for orotate was only about 1% of that for succinate and about six times that for aspartate.…”

Section: Vol 182 2000mentioning

confidence: 99%

“…The least efficient inhibitor of orotate transport within this group was aspartate, which inhibited orotate transport significantly only when tested at 10 mM. Watson et al (19) found that aspartate was not able to inhibit succinate uptake even at very high concentrations, probably because the affinity of DctA for succinate was so much greater than its affinity for aspartate.…”

Section: Vol 182 2000mentioning

confidence: 99%

“…Succinate, malate, fumarate, and aspartate are considered to be substrates for the Dct system (19). Other compounds, including D-lactate, 2-methylsuccinate, 2,2-or 2,3-dimethylsuccinate, acetoacetate, ␤-hydroxybutyrate, mercaptosuccinate, ␣-ketoglutarate, and itaconate, are either substrates or potential substrates for DctA (4,10,11).…”

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New Substrates for the Dicarboxylate Transport System of Sinorhizobium meliloti

Yurgel¹,

Mortimer²,

Rogers³

et al. 2000

J Bacteriol

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The dicarboxylate transport (Dct) system of Sinorhizobium meliloti, which is essential for a functional nitrogen-fixing symbiosis, has been thought to transport only dicarboxylic acids. We show here that the permease component of the Dct system, DctA, can transport orotate, a monocarboxylic acid, with an apparent K m of 1.7 mM and a V max of 163 nmol min ؊1 per mg of protein in induced cells. DctA was not induced by the presence of orotate. The transport of orotate was inhibited by several compounds, including succinamic acid and succinamide, which are not dicarboxylic acids. The dicarboxylic acid maleate (cis-butenedioic acid) was not an inhibitor of orotate transport, which suggests that it was not recognized by DctA. However, maleate was an excellent inducer of DctA expression. Our evaluation of 17 compounds as inducers and inhibitors of transport suggests that substrates recognized by S. meliloti DctA must have appropriately spaced carbonyl groups and an extended conformation, while good inducers are more likely to have a curved conformation.Soil bacteria belonging to the genera Sinorhizobium, Rhizobium, Bradyrhizobium, and Azorhizobium can form symbiotic associations with leguminous plants. The bacteria elicit the formation of specialized root organs called nodules, in which they reduce atmospheric dinitrogen, and provide the resulting ammonia to the plant. Symbiotic nitrogen fixation requires a large energy input. To provide this energy, the host plant supplies organic compounds such as sucrose, which are transported to the nodules and converted to substrates supplied to the bacteroids (17). The tricarboxylic acid (TCA) cycle intermediates succinate, malate, and fumarate are likely to be the major carbon sources for rhizobial bacteroids in the nodule (20). It is thought that these compounds are imported into the bacteroids using the rhizobial dicarboxylate transport (Dct) system, which in Sinorhizobium meliloti is encoded by three genes located on megaplasmid II, dctA, dctB, and dctD (20). The dctA gene codes for a high-affinity permease. dctA mutants produce nodules that are symbiotically ineffective, and bacteroids from these nodules are unable to transport dicarboxylates (4, 20). The dctB and dctD genes encode a two-component regulatory system, which activates the transcription of dctA in response to the presence of dicarboxylates in the periplasm, where the sensor domain of DctB is located (12, 18). S. meliloti DctA participates in the regulation of its inductiondctA::phoA fusions are induced to a very high level unless there is an active DctA protein in the cell (22).Succinate, malate, fumarate, and aspartate are considered to be substrates for the Dct system (19). Other compounds, including D-lactate, 2-methylsuccinate, 2,2-or 2,3-dimethylsuccinate, acetoacetate, ␤-hydroxybutyrate, mercaptosuccinate, ␣-ketoglutarate, and itaconate, are either substrates or potential substrates for DctA (4, 10, 11). Recently, a study examining fluoroorotic acid (FOA) resistance in Salmonella enterica serovar Typhimuri...

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Vol 182 2000mentioning

confidence: 99%

Section: Vol 182 2000mentioning

confidence: 99%

mentioning

confidence: 99%

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