Biology:Formate-nitrite transporter
| Form_Nir_trans | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | Form_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]
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:
- FocA and FocB (TC#s 1.A.16.1.1 and 1.A.16.1.2, respectively), from Escherichia coli, transporters involved in the bidirectional transport of formate.
- FdhC, from Methanobacterium maripaludis (TC# 1.A.16.2.3) and Methanothermobacter thermoformicicum (TC# 1.A.16.2.1), a probable formate transporter.
- NirC, from E. coli (TC# 1.A.16.3.1), a probable nitrite transporter.
- Nar1 (TC# 1.A.16.2.4) of Chlamydomonas reinhardtii (Chlamydomonas smithii), a nitrite uptake porter of 355 amino acyl residues.
- B. subtilis hypothetical protein YwcJ (ipa-48R) (TC# 1.A.16.3.2).
References
- ↑ "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. 1993-01-01. doi:10.3109/10409239309086796. PMID 8325040.
- ↑ "Phylogenetic characterization of the MIP family of transmembrane channel proteins". The Journal of Membrane Biology 153 (3): 171–80. October 1996. doi:10.1007/s002329900120. PMID 8849412.
- ↑ "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. March 1994. doi:10.1111/j.1365-2958.1994.tb00375.x. PMID 8022272.
- ↑ 4.0 4.1 "Structure of the formate transporter FocA reveals a pentameric aquaporin-like channel". Nature 462 (7272): 467–72. November 2009. doi:10.1038/nature08610. PMID 19940917. Bibcode: 2009Natur.462..467W.
- ↑ Saier, MH Jr.. "1.A.16 The Formate-Nitrite Transporter (FNT) Family". Saier Lab Bioinformatics Group / SDSC. http://www.tcdb.org/search/result.php?tc=1.A.16#ref9123.
- ↑ "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. February 2010. doi:10.1111/j.1574-6968.2009.01862.x. PMID 20041954.
- ↑ "pH-dependent gating in a FocA formate channel". Science 332 (6027): 352–4. April 2011. doi:10.1126/science.1199098. PMID 21493860. Bibcode: 2011Sci...332..352L.
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