Sodium/phosphate cotransporter
The sodium/phosphate cotransporter is a member of the phosphate:Na+ symporter (PNaS) family within the TOG Superfamily of transport proteins as specified in the Transporter Classification Database.
Contents
Nomenclature
The sodium/phosphate cotransporter is also known as:
- Na+-Pi cotransport protein (NaPi-2a),
- Sodium-dependent phosphate transporter, or
- Phosphate:Na+ symporter.
PNaS family
The Phosphate:Na+ Symporter (PNaS) family (TC# 2.A.58) includes several closely related, functionally characterized, sodium-dependent, inorganic phosphate (Pi) transporter (NPT) proteins from mammals. Other organisms that possess PNaS family members include many eukaryotic, bacterial and archaeal phyla. A bacterial sodium:phosphate symporter, NptA of Vibrio cholerae has been functionally characterized.[1]
The well-characterized mammalian proteins are found in renal (IIa isoform) and intestinal (IIb isoform) brush border membranes and are about 640 amino acyl residues long with 8-12 putative TMSs. The N- and C-termini both reside in the cytoplasm, and a large hydrophilic loop is localized between trans-membrane segments (TMSs) 3 and 4. While IIa isoforms are pH-dependent, IIb isoforms are found to be pH-independent.[2] The IIa sodium phosphate symporter isoform is a functional monomer,[3] but it interacts with PDZ proteins which probably mediate apical sorting, parathyroid hormone-controlled endocytosis and/or lysosomal sorting of internalized transporter.[4][5]
Transport reaction
The transport reaction catalyzed by the mammalian proteins is:[4]
- Pi (out) + 3 Na+ (out) ⇌ Pi (in) + 3 Na+ (in).
Human PNaS proteins
There are several known sodium-dependent phosphate transporters found in humans. For example, the protein 2A is encoded by the solute carrier family 34, member 1 (SLC34A1) gene.[6] and fascilitates uptake of phosphate for normal cellular functions including cellular metabolism, signal transduction, and nucleic acid and lipid synthesis. The PNaS family is also called the SLC34 family.
Other known sodium-dependent phosphate transporters found in humans include (but are not limited to):
- Sodium-Phosphate Cotransporter Proteins, Type I:
- Sodium-Phosphate Cotransporter Proteins, Type II:
- Sodium-Phosphate Cotransporter Proteins, Type III:
See also
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References
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Further reading
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External links
- Transporter Classification Database
- Sodium-Phosphate Cotransporter Proteins at the US National Library of Medicine Medical Subject Headings (MeSH)
