General overview:
KefC is a glutathione-gated K(+)-efflux system that is widespread in Gram-negative bacteria and which plays a role in the protection of cells from the toxic effects of electrophilic reagents.KefC protein is composed of one or more identical subunits that interact in the membrane.KefB and KefC systems are gated by glutathione metabolites (such as N-ethylmaleimide (NEM)) and that the degree to which they are activated is dependent upon the nature of the substituent on the sulphydryl group.
These two genes encode the major paths for NEM-stimulated efflux. However, neither efflux system appears to be a significant path of K+ efflux produced by high turgor pressure, by alkalinization of the cytoplasm, or by addition of high concentrations of 2,4-dinitrophenol. Therefore, this species must have at least one other system, besides those encoded by kefB and kefC, capable of mediating a high rate of K+ efflux. The high, spontaneous rate of K+ efflux characteristic of the kefC121 mutation increases further when the strain is treated with NEM. Therefore, the mutational defect that leads to spontaneous efflux in this strain does not abolish the site(s) responsible for the action of NEM. It was also shown that KefA is a cation-specific channel involved in osmotic adaptation and is functionally coupled to mechanosensitive channels in the cytoplasmic membrane of Escherichia coli.
We can expect that homologs to KefC,B,KL are responsible for glutathione dependent efflux in other bacteria as weel.
We included several other potassium efflux and uptake related function into this SS to have a more general pisture about potassium homeostases in those organisms.
KefA, MSC may be responsible for mechanosensitive potassium efflux,
kup (high sensitive K intake system) and TrkA -low sensetivity homologs may be induced by potassium deprivation. The latter is also required for serum, protamine, and some antibiotics resistance in a number of pathogenes.
Associated functions ( from gene coupling) are also included in this subsystem. You can avoid looking at them by selecting a subset 'main_K_related_functions')

(For additional information see: J Membr Biol. 1996 Mar;150(2):143-52.coli.
Mol Microbiol. 2002 Jan;43(2):521-36.)


References and additional notes:

Elmore MJ, Lamb AJ, Ritchie GY, Douglas RM, Munro A, Gajewska A, Booth IR.
Activation of potassium efflux from Escherichia coli by glutathione metabolites.
Mol Microbiol. 1990 Mar;4(3):405-12.

DNA Seq. 2002 Dec;13(6):375-81.
Cloning and characterization of a gene encoding glutathione-regulated potassium-efflux system protein KefKL from the endosymbiont Wolbachia.

Kang L, Zhu H, Cheng Q, Zhou W, Sun L, Cai L, Ma X, Chen C, Zhao S, Li C.
Mol Microbiol. 1991 Mar;5(3):607-16.
The cloning and DNA sequence of the gene for the glutathione-regulated potassium-efflux system KefC of Escherichia coli.

Munro AW, Ritchie GY, Lamb AJ, Douglas RM, BoothIR.
Low affinity K-efflux (TrkA) and K-peptide transporter:sap_operon (alternative K transporters) http://www.pubmedcentral.gov/articlerender.fcgi?tool=pmcentrez&artid=395316

YRKL-homology to KefF, other clusters. Function??
There are flavodoxines in KefF clusters as well

Identification of an Ancillary Protein, YabF, Required for Activity of the KefC Glutathione-Gated Potassium Efflux System in Escherichia coli.
Miller S, Ness LS, Wood CM, Fox BC, Booth IR.
J Bacteriol. 2000 Nov; 182(22): 6536-6540.

Nucleotide sequence and 3'-end deletion studies indicate that the K(+)-uptake protein kup from Escherichia coli is composed of a hydrophobic core linked to a large and partially essential hydrophilic C terminus.Schleyer M, Bakker EP.J Bacteriol. 1993 Nov; 175(21): 6925-6931.
PMCID: 206818

Membrane topology and multimeric structure of a mechanosensitive channel protein of Escherichia coli.
Blount P, Sukharev SI, Moe PC, Schroeder MJ, Guy HR, Kung C.
EMBO J. 1996 Sep 16; 15(18): 4798-4805.

McLaggan D, Jones MA, Gouesbet G, Levina N, Lindey S, Epstein W, Booth IR. Analysis of the kefA2 mutation suggests that KefA is a cation-specific channel involved in osmotic adaptation in Escherichia coli.
Mol Microbiol. 2002 Jan;43(2):521-36.

Cui C, Adler J. Effect of mutation of potassium-efflux system, KefA, on mechanosensitive channels in the cytoplasmic membrane of Escherichia coli.
J Membr Biol. 1996 Mar;150(2):143-52.

Chen YC, Chuang YC, Chang CC, Jeang CL, Chang MC. A K+ yptake protein, TrkA, is required for serum, protamine, and polymyxin B resistance in Vibrio vulnificus.
Infect Immun. 2004 Feb;72(2):629-36.

In Yersinia and Serratia there are no kefC. Homolog of KefG: NAD(P)H oxidoreductase YRKL (EC 1.6.99.-) ; Putative NADPH-quinone reductase (modulator of drug activity B) ; Flavodoxin 2 is clustered to anaerobic functions:Ribonucleotide reductase of class III (anaerobic). KefC is expected to be upregulated anaerobically in correlation with FNR activation (??).

Nitric oxide effect is also linked to Zn metabolism alterations, as it dismiss Zn from Zn-containing enzymes.(One of many references: Bossy-Wetzel E, Talantova MV, Lee WD, Scholzke MN, Harrop A, Mathews E, Gotz T, Han J, Ellisman MH, Perkins GA, Lipton SA. Crosstalk between nitric oxide and zinc pathways to neuronal cell death involving mitochondrial dysfunction and p38-activated K+ channels.) There is Hypothetical Zn-containing oxidoreductase in FNR-like cluster. I annotated it as:Bifunctional protein: zinc-containing alcohol dehydrogenase; quinone oxidoreductase ( NADPH:quinone reductase) (EC 1.1.1.-) ; Similar to arginate lyase (The last annotation comes from uniprot and I desided to keep it). Function of this enzyme??

cAMP and PDE are coupled to Sulfate , sulfide reductases in Vibrio and Pho.pro.

MarR and NNR-cases of fusion!

Rubredoxin=-Rubredoxin-type Fe(Cys)4 protein

Arginase: Pantopoulos K, Hentze MW. Related Articles, Links
Rapid responses to oxidative stress mediated by iron regulatory protein.
EMBO J. 1995 Jun 15;14(12):2917-24.

cAMP:
Cell. 2004 Nov 24;119(5):615-27. Structural basis of ligand activation in a cyclic nucleotide regulated potassium channel.

Clayton GM, Silverman WR, Heginbotham L, Morais-Cabral JH.

Here we describe the initial functional characterization of a cyclic nucleotide regulated ion channel from the bacterium Mesorhizobium loti and present two structures of its cyclic nucleotide binding domain, with and without cAMP. The domains are organized as dimers with the interface formed by the linker regions that connect the nucleotide binding pocket to the pore domain. Together, structural and functional data suggest the domains form two dimers on the cytoplasmic face of the channel. We propose a model for gating in which ligand binding alters the structural relationship within a dimer, directly affecting the position of the adjacent transmembrane helices.

Neuron. 1994 May;12(5):1097-109. Regulation of Shaker K+ channel inactivation gating by the cAMP-dependent protein kinase

Variant code:
1-KefA,B,C,G,F, TrkA,MSC,kup.
Other numbers: variations of lesser set of functions