Table 1. Bacterial K+-translocating systems.
Summary of known bacterial K+-translocating systems highlighting the individual composition, hypothesized transport mode and direction, and representative structures. Putative transport modes are indicated with *. No transport direction is indicated for channels, as by definition ion fluxes are dictated by the electrochemical gradient.
| System | Subunit | Description, family | Transport mode (incl. dependency, direction) | Structures (PDB/EMDB) |
|---|---|---|---|---|
| Ion channel | ||||
| KcsA [150] | 2-TM potassium channel | Voltage-dependent channel | 3EFF (full-length, closed) 1K4C (closed, conductive) 1K4D (closed, inactive) 5VK6 (open, conductive) 5VKE (open, inactive) |
|
| MthK [77, 151] | 2-TM potassium channel with fused and soluble RCK domain | Ca2+-gated channel | 6U6D (Ca2+-free closed) 6UX7,6UXA,6UXB (Ca2+-bound open) 6U68,6U6E,6U6H (Ca2+-bound open-inactivated) |
|
| GsuK [71] | 2-TM potassium channel with dual fused RCK domain | Ca2+- & ADP/NAD+-gated channel | 4GX5 (Ca2+-bound closed) | |
| EcKch | 6-TM potassium channel with fused and soluble RCK domain | Ligand-gated channel* | 1ID1 (RCK domain) | |
| HpKch | 2-TM potassium channel with fused and soluble RCK domain | Ligand-gated channel* | ||
| YugO | 2-TM potassium channel with fused RCK domain | Ligand-gated channel* | ||
| TrkAH [6] | TrkA | RCK subunit (cytosolic) | ATP-, proton- (& c-di-AMP-) gated channel | 4J9U (ADP-bound) 6V4K (ATP-bound) |
| TrkH | Translocating subunit (TM), SKT family | |||
| KtrAB [5, 100] | KtrA | RCK subunit (cytosolic) | ATP-, Na+- (& c-di-AMP-) gated, pmf-dependent channel | 4J7C (ATP-bound) EM-3405 (ADP-bound) 4XTT (c-di-AMP-bound KtrA C-term) |
| KtrB | Translocating subunit (TM), SKT family | |||
| KtrCD [82, 141, 152] | KtrC | RCK subunit (cytosolic) | ATP- (& c-di-AMP) gated, glutamate-dependent channel | 6I8V (ATP-bound KtrC) |
| KtrD | Translocating subunit (TM), SKT family | |||
| Primary active transporter | ||||
| KdpFABC [7, 20] | KdpF | Small lipid-like subunit | K+ pump (uptake) | 5MRW (E1 state) 6HRA (E1 state) 6HRB (E2 state) |
| KdpA | Channel-like subunit, SKT family | |||
| KdpB | P-type ATPase subunit | |||
| KdpC | Periplasmatically oriented single TM subunit | |||
| Secondary active transporter | ||||
| KimA [8, 132, 152–154] | KUP family | K+/H+ symporter (uptake) | 6S3K | |
| Kup (TrkD) [127, 155] | KUP family | K+/H+ symporter (uptake) | ||
| Kef system [138, 140] | KefB/C | Cation:Proton antiporter 2 with fused RCK/KTN domain | Glutathione-gated K+/H+ antiporter (export) |
3L9W (KefC_RCK-KefF) |
| KefG/F | Flavoprotein | |||
| YjbQ(CpaA)[132, 156] |
Cation:Proton antiporter 2 | K+/H+ antiport (export) | 5F29 (RCK domain) | |
| KhtSTU [140, 157, 158] | KhtS | Antiporter modulator of KhtU | Ligand-gated K+/H+ antiport* (export) | |
| KhtT | C-terminal RCK protein | |||
| KhtU | Cation:Proton antiporter 2 | |||