2g29
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Revision as of 08:47, 21 November 2007
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crystal structure of the periplasmic nitrate-binding protein NrtA from Synechocystis PCC 6803
Overview
Cyanobacteria, blue-green algae, are the most abundant autotrophs in, aquatic environments and form the base of all aquatic food chains by, fixing carbon and nitrogen into cellular biomass. The single most, important nutrient for photosynthesis and growth is nitrate, which is, severely limiting in many aquatic environments particularly the open, ocean. It is therefore not surprising that NrtA, the solute-binding, component of the high-affinity nitrate ABC transporter, is the single-most, abundant protein in the plasma membrane of these bacteria. Here, we, describe the structure of a nitrate-specific receptor, NrtA from, Synechocystis sp. PCC 6803, complexed with nitrate and determined to a, resolution of 1.5 A. NrtA is significantly larger than other, oxyanion-binding proteins, representing a previously uncharacterized class, of transport proteins. From sequence alignments, the only other, solute-binding protein in this class is CmpA, a bicarbonate-binding, protein. Therefore, these organisms created a solute-binding protein for, two of the most important nutrients: inorganic nitrogen and carbon. The, electrostatic charge distribution of NrtA appears to force the protein off, the membrane while the flexible tether facilitates the delivery of nitrate, to the membrane pore. The structure not only details the determinants for, nitrate selectivity in NrtA but also the bicarbonate specificity in CmpA., Nitrate and bicarbonate transport are regulated by the cytoplasmic, proteins NrtC and CmpC, respectively. Interestingly, the residues lining, the ligand binding pockets suggest that they both bind nitrate. This, implies that the nitrogen and carbon uptake pathways are synchronized by, intracellular nitrate and nitrite.
About this Structure
2G29 is a Single protein structure of sequence from Synechocystis sp. with NO3 as ligand. Full crystallographic information is available from OCA.
Reference
Atomic structure of a nitrate-binding protein crucial for photosynthetic productivity., Koropatkin NM, Pakrasi HB, Smith TJ, Proc Natl Acad Sci U S A. 2006 Jun 27;103(26):9820-5. Epub 2006 Jun 15. PMID:16777960
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