TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
*2.A.38.1.1









K+ uptake transporter (K+:H+ symporter), TrkHA. The 3-d structure of TrkH is known (Cao et al. 2011).  Molecular dynamics simulations of TrkH have been reported (Domene and Furini, 2012).  TrkA, which forms a tertameric ring that needs to bind ATP to activate transport, interacts with the Enzyme IIANtr of the PTS (TC# 4.A) which inhibits transport (Lee et al. 2007).

Bacteria
Proteobacteria
TrkHA of E. coli
TrkH (P0AFZ7)
TrkA (P23868)
*2.A.38.1.2









K+ uptake transporter, TrkIA (Km=1 mM) (Kraegeloh et al., 2005)
Bacteria
Proteobacteria
TrkIA of Halomonas elongata
TrkI (AAR91793)
TrkA (AAR91791)
*2.A.38.1.3









K+ uptake transporter, TrkHA (Km=3 mM) (Kraegeloh et al., 2005)
Bacteria
Proteobacteria
TrkHA of Halomonas elongata
TrkH (Q6T3V7)
TrkA (Q6T3V8)
*2.A.38.1.4









Two component K+ transporter, TrkA (TM1088A/B/TM1089) (The x-ray structure (2G1U_A) of TM1088A, the nucleotide-binding subunit, shows a Rossmann fold, and the crystal structure has AMP tightly bound to the GXGXXG motif. TM1089 is the membrane subunit) (Johnson et al., 2009).
Bacteria
Thermotogae
TrkA of Thermotoga maritima
TM1088A (gi #93279835)
TM1089 (Q9X0H4)
*2.A.38.1.5









Cation (K+,Rb+>Na+,Li+) transporter, TrkH. (A homodimer with each monomer containing an ion permeation pathway. 3d structure known (PDB acc#3PJZ; Cao et al., 2011).

Bacteria
Proteobacteria
TrkH of Vibrio parahaemolyticus (Q87TN7)
*2.A.38.1.6









Trk system potassium uptake protein TrkG
Bacteria
Proteobacteria
TrkG of Escherichia coli
*2.A.38.2.1









High affinity K+ transporter (K+:H+ symporter)
Eukaryota
Fungi
Trk1 of Saccharomyces cerevisiae
*2.A.38.2.2









Probable K+ uniporter, Trk1. Synthesized constitutively at low levels; synthesis is insensitive to extracellular K+ or the expression of Trk1 (2.A.38.2.2) (Rivetta et al. 2013).

Eukaryota
Fungi
Trk1 of Neurospora crassa
*2.A.38.2.3









Low affinity K+ transporter, Trk2 (Bertl et al., 2003)
Eukaryota
Fungi
Trk2 of Saccharomyces cerevisiae
*2.A.38.2.4









The K+ uptake transporter, Trk1 (Prista et al., 2007)
Eukaryota
Fungi
DhTrk1 of Debaryomyces hansenii (Q6BYD8)
*2.A.38.2.5









K+ and Na+ channel protein Trk1 (inward rectifying current; a single file pore mechanism is suggested (Corratgé et al., 2007).

Eukaryota
Fungi
Trk1 of Hebeloma cylindrosporum (A4H1L2)
*2.A.38.3.1









High affinity K+ transporter (K+:Na+ symporter) (Kato et al., 2007).

Eukaryota
Viridiplantae
Hkt1 of Triticum aestivum
*2.A.38.3.2









K+ (high affinity) Na+ -selective (low affinity) uptake symporter, AtHKT1 (does not catalyze recirculation from shoots to roots as proposed by Berthomieu et al., 2003, but mediates Na+ unloading from the xylem sap and thereby protects plant leaves from toxic Na+ over accumulation (Sunarpi et al. 2005). Kato et al. (2007) have reported that AtHKT1 is a Na+ uniporter.

Eukaryota
Viridiplantae
AtHKT1 of Arabidopsis thaliana (Q84TI7)
*2.A.38.3.3









K+ or Na+ uptake uniporter or Na+-K+ uptake symporter, HKT1. (Banuelos et al, 2008). The high affinity HKT2;4 paralogue can function as a Ca2+-permeable cation channel (Lan et al., 2010).

Eukaryota
Viridiplantae
HKT1 of Oryza sativa (Q0D9S3)
*2.A.38.3.4









The Na+:K+ cotransporter, HKT2;4. (also transports Mg2+ and Ca2+ in the absence of K+) (Horie et al., 2011).

Eukaryota
Viridiplantae
The HKT2;4 protein of Oryza sativa (A3FFK5)
*2.A.38.3.5









Cation transporter HKT4 (OsHKT4)
Eukaryota
Viridiplantae
HKT4 of Oryza sativa
*2.A.38.4.1









Low affinity K+ transporter, KtrII (K+:Na+ symporter)
Bacteria
Firmicutes
NtpJ of Enterococcus hirae
*2.A.38.4.2









High affinity (Km <50 μM) KtrA binds ATP to a β-α-β-Rossman fold. Other nucleotides bound, but only ATP bound with high affinity and changed the conformation of KtrA so that KtrA and KtrB associate (Kroning et al., 2007) in vivo. Both ATP and ΔΨ were required for transport activity. K+ uptake may occur by a Na+:K+ symport mechanism.  However, one region of KtrB, the transmembrane helix (M(2C); 40aas long) seems to control K+ transport non-coordinately with Na+ symport (Haenelt et al., 2010). M2C2 may form a flexible "gate" controlling K+ translocation at the cytoplasmic side of KtrB (Hänelt et al. 2010).  M(2C2) seems to be required for the interaction between KtrA and KtrB.

Bacteria
Proteobacteria
KtrAB of Vibrio alginolyticus
*2.A.38.4.3









Low affinity (1 mM) K+ uptake transporter, KtrAB. Evidence for structural similarities between potassium channels and KtrB proteins in the extracellular half of the molecule and differences in the cytoplasmic regions has been obtained (Albright et al., 2007). This system is responsible for K+ accumulation in the cell cytoplasm, allowing oscillatory release of K+ from a biofilm through the BikC (YugO) K+ channel for the attraction of other bacteria (both of the same and different species) to the biofilm (Humphries et al. 2017).

Bacteria
Firmicutes
KtrAB (YuaA/YubG) of Bacillus subtilis
*2.A.38.4.4









Very low affinity (10 mM) K+ uptake transporter, KtrCD
Bacteria
Firmicutes
KtrCD (YkqB/YkrM) of Bacillus subtilis
*2.A.38.4.5









The Na+-dependent K+ uptake transporter, KtrABE, required for adaption to salinity stress and high osmolarity (Zulkifli et al., 2010). KtrB alone confers low K+ uptake activity; KtrA+KtrE are required for Na+ dependency and higher K+ uptake rates.

Bacteria
Cyanobacteria
KtrABE of Synechocystis sp. strain PPC6803
KtrA (Q55496)
KtrB (P73949)
KtrE (P73948)
*2.A.38.4.6









K+ uptake system, KtrABD.  S. aureus devoid of the Ktr system became sensitive to hyperosmotic conditions, exhibited a hyperpolarized plasma membrane, and increased susceptibility to aminoglycoside antibiotics and cationic antimicrobials. In contrast to other organisms, the S. aureus Ktr system was shown to be important for low-K+ growth under alkaline conditions but played only a minor role in neutral and acidic conditions. In a mouse competitive index model of bacteraemia, the ktrA mutant was significantly outcompeted by the parental strain (Gries et al. 2013).

Bacteria
Firmicutes
KtrABD of Staphylococcus aureus
*2.A.38.5.1









The Na+-independent K+ uptake transporter, HKT1 (Mosimann et al., 2010).

Eukaryota
Kinetoplastida
TbHKT1 of Trypanosoma brucei (Q38BH0)