Formate-nitrite transporter

Last updated
Form_Nir_trans
Identifiers
SymbolForm_Nir_trans
Pfam PF01226
InterPro IPR000292
PROSITE PDOC00769
TCDB 2.A.44
OPM superfamily 7
OPM protein 3tdp

The Formate-Nitrite Transporter (FNT) Family belongs to the Major Intrinsic Protein (MIP) Superfamily. [1] [2] FNT family members have been sequenced from Gram-negative and Gram-positive bacteria, archaea, yeast, plants and lower eukaryotes. The prokaryotic proteins of the FNT family probably function in the transport of the structurally related compounds, formate and nitrite. [3]

Contents

Structure

With the exception of the yeast protein (627 amino acyl residues), all characterized members of the family are of 256-285 residues in length and exhibit 6-8 putative transmembrane α-helical spanners (TMSs). In one case, that of the E. coli FocA (TC# 1.A.16.1.1) protein, a 6 TMS topology has been established. [4] The yeast protein has a similar apparent topology but has a large C-terminal hydrophilic extension of about 400 residues.

FocA of E. coli is a symmetric pentamer, with each subunit consisting of six TMSs. [4]

Phylogeny

The phylogenetic tree shows clustering according to function and organismal phylogeny. The putative formate efflux transporters (FocA; TC#s 1.A.16.1.1 and 1.A.16.1.3) of bacteria associated with pyruvate-formate lyase (pfl) comprise cluster I; the putative formate uptake permeases (FdhC; TC#s 1.A.16.2.1 and 1.A.16.2.3) of bacteria and archaea associated with formate dehydrogenase comprise cluster II; the nitrite uptake permeases (NirC, TC#s 1.A.16.2.5, 1.A.16.3.1, and 1.A.16.3.4) of bacteria comprise cluster III, and a yeast protein comprises cluster IV. [5]

Function

The energy coupling mechanisms for proteins of the FNT family have not been extensively characterized. HCO−
2 and NO−
2 uptakes may be coupled to H+ symport. HCO−
2 efflux may be driven by the membrane potential by a uniport mechanism or by H+ antiport. FocA of E. coli catalyzes bidirectional formate transport and may function by a channel-type mechanism. [6]

FocA, transports short-chain acids. FocA may be able to switch its mode of operation from a passive export channel at high external pH to a secondary active formate/H+ importer at low pH. The crystal structure of Salmonella typhimurium FocA at pH 4.0 shows that this switch involves a major rearrangement of the amino termini of individual protomers in the pentameric channel. [7] The amino-terminal helices open or block transport in a concerted, cooperative action that indicates how FocA is gated in a pH-dependent way. Electrophysiological studies show that the protein acts as a specific formate channel at pH 7.0 and that it closes upon a shift of pH to 5.1.

Transport Reaction

The probable transport reactions catalyzed by different members of the FNT family are:

(1) RCO−
2 or NO−
2 (out) ⇌ RCO−
2 or NO−
2 (in),

(2) HCO−
2 (in) ⇌ HCO−
2 (out),

(3) HS− (out) ⇌ HS− (in).

Members

A representative list of the currently classified members belonging to the FNT family can be found in the Transporter Classification Database. Some characterized members include:

Related Research Articles

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  1. The aquaporins (AQPs) are water selective.
  2. The aquaglyceroporins are permeable to water, but also to other small uncharged molecules such as glycerol.
  3. The third subfamily, with little conserved amino acid sequences around the NPA boxes, include 'superaquaporins' (S-aquaporins).

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Mercury transporter

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4:HCO−
3 exchange, or more generally, anion:anion antiport. For example, the mouse homologue, SLC26A6, can transport sulfate, formate, oxalate, chloride and bicarbonate, exchanging any one of these anions for another. A cyanobacterial homologue can transport nitrate. Some members can function as channels. SLC26A3 and SLC26A6 can function as carriers or channels, depending on the transported anion. In these porters, mutating a glutamate, also involved in transport in the CIC family, created a channel out of the carrier. It also changed the stoichiometry from 2Cl−/HCO−
3 to 1Cl−/HCO−
3.

Natural resistance-associated macrophage protein Family of transport proteins

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  2. One (PST) specific for polysaccharides and/or their lipid-linked precursors in prokaryotes - (TC# 2.A.66.2) The Polysaccharide Transport (PST) Family
  3. One (OLF) specific for lipid-linked oligosaccharide precursors of glycoproteins in eukaryotes - (TC# 2.A.66.3) The Oligosaccharidyl-lipid Flippase (OLF) Family
  4. One (MVF) lipid-peptidoglycan precursor flippase involved in cell wall biosynthesis - (TC# 2.A.66.4) The Mouse Virulence Factor (MVF) Family
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References

  1. ↑ Reizer J, Reizer A, Saier MH (1993-01-01). "The MIP family of integral membrane channel proteins: sequence comparisons, evolutionary relationships, reconstructed pathway of evolution, and proposed functional differentiation of the two repeated halves of the proteins". Critical Reviews in Biochemistry and Molecular Biology. 28 (3): 235–57. doi:10.3109/10409239309086796. PMID   8325040.
  2. ↑ Park JH, Saier MH (October 1996). "Phylogenetic characterization of the MIP family of transmembrane channel proteins". The Journal of Membrane Biology. 153 (3): 171–80. doi:10.1007/s002329900120. PMID   8849412. S2CID   1559932.
  3. ↑ Suppmann B, Sawers G (March 1994). "Isolation and characterization of hypophosphite--resistant mutants of Escherichia coli: identification of the FocA protein, encoded by the pfl operon, as a putative formate transporter". Molecular Microbiology. 11 (5): 965–82. doi:10.1111/j.1365-2958.1994.tb00375.x. PMID   8022272. S2CID   6425651.
  4. 1 2 Wang Y, Huang Y, Wang J, Cheng C, Huang W, Lu P, Xu YN, Wang P, Yan N, Shi Y (November 2009). "Structure of the formate transporter FocA reveals a pentameric aquaporin-like channel". Nature. 462 (7272): 467–72. Bibcode:2009Natur.462..467W. doi:10.1038/nature08610. PMID   19940917. S2CID   4370839.
  5. ↑ Saier, MH Jr. "1.A.16 The Formate-Nitrite Transporter (FNT) Family". Transporter Classification Database. Saier Lab Bioinformatics Group / SDSC.
  6. ↑ Falke D, Schulz K, Doberenz C, Beyer L, Lilie H, Thiemer B, Sawers RG (February 2010). "Unexpected oligomeric structure of the FocA formate channel of Escherichia coli : a paradigm for the formate-nitrite transporter family of integral membrane proteins". FEMS Microbiology Letters. 303 (1): 69–75. doi: 10.1111/j.1574-6968.2009.01862.x . PMID   20041954.
  7. ↑ Lü W, Du J, Wacker T, Gerbig-Smentek E, Andrade SL, Einsle O (April 2011). "pH-dependent gating in a FocA formate channel". Science. 332 (6027): 352–4. Bibcode:2011Sci...332..352L. doi:10.1126/science.1199098. PMID   21493860. S2CID   20059830.
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