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PMID:10557362
| Citation |
Omata, T, Price, GD, Badger, MR, Okamura, M, Gohta, S and Ogawa, T (1999) Identification of an ATP-binding cassette transporter involved in bicarbonate uptake in the cyanobacterium Synechococcus sp. strain PCC 7942. Proc. Natl. Acad. Sci. U.S.A. 96:13571-6 |
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| Abstract |
Exposure of cells of cyanobacteria (blue-green algae) grown under high-CO(2) conditions to inorganic C-limitation induces transcription of particular genes and expression of high-affinity CO(2) and HCO(3)(-) transport systems. Among the low-CO(2)-inducible transcription units of Synechococcus sp. strain PCC 7942 is the cmpABCD operon, encoding an ATP-binding cassette transporter similar to the nitrate/nitrite transporter of the same cyanobacterium. A nitrogen-regulated promoter was used to selectively induce expression of the cmpABCD genes by growth of transgenic cells on nitrate under high CO(2) conditions. Measurements of the initial rate of HCO(3)(-) uptake after onset of light, and of the steady-state rate of HCO(3)(-) uptake in the light, showed that the controlled induction of the cmp genes resulted in selective expression of high-affinity HCO(3)(-) transport activity. The forced expression of cmpABCD did not significantly increase the CO(2) uptake capabilities of the cells. These findings demonstrated that the cmpABCD genes encode a high-affinity HCO(3)(-) transporter. A deletion mutant of cmpAB (M42) retained low CO(2)-inducible activity of HCO(3)(-) transport, indicating the occurrence of HCO(3)(-) transporter(s) distinct from the one encoded by cmpABCD. HCO(3)(-) uptake by low-CO(2)-induced M42 cells showed lower affinity for external HCO(3)(-) than for wild-type cells under the same conditions, showing that the HCO(3)(-) transporter encoded by cmpABCD has the highest affinity for HCO(3)(-) among the HCO(3)(-) transporters present in the cyanobacterium. This appears to be the first unambiguous identification and description of a primary active HCO(3)(-) transporter. |
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| Keywords |
ATP-Binding Cassette Transporters/genetics; ATP-Binding Cassette Transporters/metabolism; Bicarbonates/metabolism; Cyanobacteria/genetics; Cyanobacteria/metabolism; Genes, Bacterial; Mutation; Sequence Deletion |
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Significance
Annotations
| Gene product | Qualifier | GO Term | Evidence Code | with/from | Aspect | Extension | Notes | Status |
|---|---|---|---|---|---|---|---|---|
|
enables |
GO:0015106: bicarbonate transmembrane transporter activity |
ECO:0000314: direct assay evidence used in manual assertion |
F |
Seeded From UniProt |
complete | |||
| GO:0015106: bicarbonate transmembrane transporter activity |
ECO:0000314: |
F |
Figure 3 shows that when a mutant placing the cmpABCD ABC transporter complex after a nitrogen-inducible promoter, the mutant took up high amounts of bicarbonate when grown in high bicarbonate media. Comparatively, the WT grown under these same conditions had a negligible uptake of bicarbonate. When grown in media containing ammonium and high amounts of bicarbonate, the mutant has low bicarbonate uptake because the transporter was not induced by nitrogen, so nothing in the cell is taking up bicarbonate. |
complete | ||||
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