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2.A.1.8.1
Nitrate/H+ symporter (K1);Nitrate/nitrite antiporter (K2).  The 3-d structure is available revealing a positively charged pathway for nitrate/nitrite lined with arginine residues with no apparent proton pathway suggesting exchange transport is the primary or sole mechanism.  The pathway is between the two halves of the protein and a rocker switch mechanism was proposed (Zheng et al. 2013).  In an in vitro reconstituted system, NarK appeared to be a nitrate/nitrite antiporter.  High-resolution crystal structures in the nitrate-bound occluded, nitrate-bound inward-open and apo inward-open states have been solved (Fukuda et al. 2015).

Accession Number:P10903
Protein Name:NarK aka NarK1-K2 aka B1223
Length:463
Molecular Weight:49693.00
Species:Escherichia coli [83333]
Number of TMSs:12
Location1 / Topology2 / Orientation3: Cell inner membrane1 / Multi-pass membrane protein2
Substrate hydron, nitrite, nitrate

Cross database links:

RefSeq: AP_001851.1    NP_415741.1   
Entrez Gene ID: 945783   
Pfam: PF07690   
BioCyc: EcoCyc:NARK-MONOMER    ECOL168927:B1223-MONOMER   
KEGG: ecj:JW1214    eco:b1223   

Gene Ontology

GO:0016021 C:integral to membrane
GO:0005886 C:plasma membrane
GO:0005452 F:inorganic anion exchanger activity
GO:0015112 F:nitrate transmembrane transporter activity
GO:0015514 F:nitrite efflux transmembrane transporter ac...
GO:0015513 F:nitrite uptake transmembrane transporter ac...
GO:0042128 P:nitrate assimilation
GO:0015706 P:nitrate transport
GO:0015707 P:nitrite transport
GO:0055085 P:transmembrane transport

References (6)

[1] “The narK gene product participates in nitrate transport induced in Escherichia coli nitrate-respiring cells.”  Noji S.et.al.   2668029
[2] “A 718-kb DNA sequence of the Escherichia coli K-12 genome corresponding to the 12.7-28.0 min region on the linkage map.”  Oshima T.et.al.   8905232
[3] “The complete genome sequence of Escherichia coli K-12.”  Blattner F.R.et.al.   9278503
[4] “Highly accurate genome sequences of Escherichia coli K-12 strains MG1655 and W3110.”  Hayashi K.et.al.   16738553
[5] “The narX and narL genes encoding the nitrate-sensing regulators of Escherichia coli are homologous to a family of prokaryotic two-component regulatory genes.”  Nohno T.et.al.   2657652
[6] “Global topology analysis of the Escherichia coli inner membrane proteome.”  Daley D.O.et.al.   15919996
Structure:
4JR9   4JRE   4U4T   4U4V   4U4W     

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Predict TMSs (Predict number of transmembrane segments)
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FASTA formatted sequence 
1:	MSHSSAPERA TGAVITDWRP EDPAFWQQRG QRIASRNLWI SVPCLLLAFC VWMLFSAVAV 
61:	NLPKVGFNFT TDQLFMLTAL PSVSGALLRV PYSFMVPIFG GRRWTAFSTG ILIIPCVWLG 
121:	FAVQDTSTPY SVFIIISLLC GFAGANFASS MANISFFFPK QKQGGALGLN GGLGNMGVSV 
181:	MQLVAPLVVS LSIFAVFGSQ GVKQPDGTEL YLANASWIWV PFLAIFTIAA WFGMNDLATS 
241:	KASIKEQLPV LKRGHLWIMS LLYLATFGSF IGFSAGFAML SKTQFPDVQI LQYAFFGPFI 
301:	GALARSAGGA LSDRLGGTRV TLVNFILMAI FSGLLFLTLP TDGQGGSFMA FFAVFLALFL 
361:	TAGLGSGSTF QMISVIFRKL TMDRVKAEGG SDERAMREAA TDTAAALGFI SAIGAIGGFF 
421:	IPKAFGSSLA LTGSPVGAMK VFLIFYIACV VITWAVYGRH SKK