Subsystem: Potassium homeostasis
This subsystem's description is:
Potassium homeostasis is one of the central attributes of any live cell. It effects membrane potential and almost all membrane-related functions, it reacts to changes in osmotic strength, pH and cell volume balancing effected processes and bringing cell to a new funtional equlibrium. Changes in potassium efflux were adopted as a downstream effector by different signaling systems.
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.
KefA, MSC may be responsible for mechanosensitive potassium efflux,
Voltage gated channels have been found in bacteria and eukarya though in the latter they are more diversed and generally more significant. Potassium voltage-gated channel subfamily B was found only in eukarya.Here we include only two members of this protein family, more as an illustration of their specific occurance.
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.
The molecular basis of potassium uptake in cyanobacteria has not been elucidated. However, genes known from other bacteria to encode potassium transporters can be identified in the genome of Synechocystis sp. strain PCC 6803. Mutants defective in kdpA and ntpJ were generated and characterized to address the role of the Kdp and KtrAB systems in this strain. KtrAB is crucial for K(+) uptake, as the DeltantpJ mutant shows slowed growth, slowed potassium uptake kinetics, and increased salt sensitivity. The DeltakdpA mutant has the same phenotype as the wild type even at limiting potassium, but a DeltakdpADeltantpJ double mutant is not viable, indicating a role of Kdp for potassium uptake when the Ktr system is not functioning.(FEBS Lett. 2003 Jul 31;548(1-3):53-8)
SKC1-the small K+ channel from Streptomyces lividans (SKC1).It behaves as a pH-gated K+ channel in which protonation of one or more residues promotes channel opening(Biochemistry. 1998 Mar 10;37(10):3229-36)
Due to a restriction of a number of major code variants to 9 our classification is pretty much arbitrary. Each combination of transporters present in an organism has a functional meaning and an unique significance.
For more information, please check out the description and the additional notes tabs, below
|Diagram||Functional Roles||Subsystem Spreadsheet||Description||Additional Notes|
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