Atomic structure of a nitrate-binding protein crucial for photosynthetic productivity

Nicole M. Koropatkin, Himadri B. Pakrasi, Thomas Smith

Research output: Contribution to journalArticle

54 Citations (Scopus)

Abstract

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 Å. 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.

Original languageEnglish (US)
Pages (from-to)9820-9825
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume103
Issue number26
DOIs
StatePublished - Jun 27 2006
Externally publishedYes

Fingerprint

Nitrates
Carrier Proteins
Bicarbonates
Nitrogen
Carbon
Cyanobacteria
Synechocystis
Food
ATP-Binding Cassette Transporters
Food Chain
Sequence Alignment
Photosynthesis
Nitrites
Static Electricity
Oceans and Seas
Biomass
Membrane Proteins
Proteins
Cell Membrane
Ligands

Keywords

  • ABC transporter
  • Carbon
  • Nitrogen assimilation
  • Regulation

ASJC Scopus subject areas

  • Genetics
  • General

Cite this

Atomic structure of a nitrate-binding protein crucial for photosynthetic productivity. / Koropatkin, Nicole M.; Pakrasi, Himadri B.; Smith, Thomas.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 103, No. 26, 27.06.2006, p. 9820-9825.

Research output: Contribution to journalArticle

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