KCNB1
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Location (UCSC) | Chr 20: 49.29 – 49.48 Mb | Chr 2: 166.94 – 167.03 Mb | |||||||
PubMed search | [3] | [4] |
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Potassium voltage-gated channel, Shab-related subfamily, member 1, also known as KCNB1 or Kv2.1, is a protein that, in humans, is encoded by the KCNB1 gene.[5][6][7]
Potassium voltage-gated channel subfamily B member one, or simply known as KCNB1, is a delayed rectifier and voltage-gated potassium channel found throughout the body. The channel has a diverse number of functions. However, its main function, as a delayed rectifier, is to propagate current in its respective location. It is commonly expressed in the central nervous system, but may also be found in pulmonary arteries, auditory outer hair cells, stem cells, the retina, and organs such as the heart and pancreas. Modulation of K+ channel activity and expression has been found to be at the crux of many profound pathophysiological disorders in several cell types.[8]
Potassium channels are among the most diverse of all ion channels in eukaryotes. With over 100 genes coding numerous functions, many isoforms of potassium channels are present in the body, but most are divided up into two main groups: inactivating transient channels and non-inactivating delayed rectifiers. Due to the multiple varied forms, potassium delayed rectifier channels open or close in response to a myriad of signals. These include: cell depolarization or hyperpolarization, increases in intracellular calcium concentrations, neurotransmitter binding, or second messenger activity such as G-proteins or kinases.[9]
Structure
The general structure of all potassium channels contain a centered pore composed of alpha subunits with a pore loop expressed by a segment of conserved DNA, T/SxxTxGxG. This general sequence comprises the selectivity of the potassium channel. Depending on the channel, the alpha subunits are constructed in either a homo- or hetero-association, creating a 4-subunit selectivity pore or a 2-subunit pore, each with accessory beta subunits attached intracellularly. Also on the cytoplasmic side are the N- and C- termini, which play a crucial role in activating and deactivating KCNB1 channels. This pore creates the main opening of the channel where potassium ions flow through.[10]
The type of pore domain (number of subunits) determines if the channel has the typical 6
Specifically, the KCNB1 delayed rectifier channel conducts a potassium current (K+). This mediates high frequency firing due to the phosphorylation sites located within the channel via kinases and a major calcium influx typical of all neurons.[11]
Kinetics
The kinetics surrounding the activation and deactivation of the KCNB1 channel is relatively unknown, and has been under considerable study. Three of the six transmembrane regions, S2, S3 and S4, contribute to the activation phase of the channel. Upon depolarization, the S4 region, which is positively charged, is moved in response to the subsequent positive charge of the depolarization. As a result of S4 movement, the negatively charged regions of S2 and S3 appear to move as well.[10] The movement of these regions causes an opening of the channel gate within regions of S5 and S6.[12] The intracellular regions of the C and N-terminus also play a crucial role in the activation kinetics of the channel. The two termini interact with one other, as the C-terminus folds around the N-terminus during channel activation. The relative movement between the N- and C- termini greatly aids in producing a conformational change of the channel necessary for channel opening. This interaction between these intracellular regions is believed to be linked with membrane-spanning regions of S1 and S6, and thus aid in the movement of S2, S3, and S4 in opening the channel.[10][12] Studies on selective mutations knocking out these intracellular termini have been shown to produce larger reductions in speed and probability of channel opening, which indicates their importance in channel activation.[10]
Function
Voltage-gated potassium (
Voltage-gated potassium channels are essential in regulating neuronal
Regulation
KCNB1 conductance is regulated primarily by oligomerization and phosphorylation. Additional forms of regulation include SUMOylation and acetylation, although the direct effect of these modifications is still under investigation. KCNB1 consensus sites in the N-terminus are not subject to glycosylation.[8]
Phosphorylation
Many proteins undergo phosphorylation, or the addition of phosphate groups to
Oligomerization
Another proposed mechanism for regulation of apoptosis is oligomerization, or the process of forming multi-protein complexes held together through disulfide bonds. Under oxidative stress, reactive oxygen species (ROS) form and act to regulate KCNB1 through oxidation. Increase in oxygen radicals directly causes formation of KCNB1 oligomers that then accumulate in the plasma membrane and initially decrease current flow.[17][18] Oligomer activation of c-Src and JNK kinases induces the initial pro-apoptotic signal, which is coupled to KCNB1 current. This further promotes the apoptosis pathway.[19] KCNB1 oligomers have been detected in the post mortem human hippocampus [20]
Blockers
Potassium delayed rectifiers have been implicated in many pharmacological uses in the investigation of biological toxins for drug development. A main component to many of the toxins with negative effects on delayed rectifiers contain cystine inhibitors that are arranged around disulfide bond formations. Many of these toxins originate from species of tarantulas. G. spatulata produces the hanatoxin, which was the first drug to be manipulated to interact with KCNB1 receptors by inhibiting the activation of most potassium voltage-gated channels. Other toxins, such as stromatoxin, heteroscordratoxin, and guangxitoxin, target the selectivity of voltage KCNB1 rectifiers, by either lowering potassium binding affinity or increasing the binding rate of potassium. This can lead to excitotoxicity, or overstimulation of postsynaptic neurons. In nature, the prey of tarantula that are injected with these endogenous toxins induces this excitotoxic effect, producing paralysis for easy capture. Physiologically, these venoms work on KCNB1 rectifier affinity by altering the channels’ voltage sensor, making it more or less sensitive to extracellular potassium concentrations.[21] KCNB1 is also susceptible to tetraethylammonium (TEA) and 4-aminopyridine (4-AP), which completely block all channel activity. TEA also works on calcium-activated potassium channels, furthering its inhibitory effects on neurons and skeletal muscle. Some isoforms of TEA are beneficial for patients with severe Alzheimer's, as blocking KCNB1 channels reduces the amount of neuronal apoptosis, thereby slowing the rate of dementia.[22] This has been attributed to the oxidative properties of the channel by ROS.[9]
Physiological Role in Disease
Neurodegenerative Disease
Oxidative damage is widely considered to play a role in neurodegenerative disorders, including Alzheimer's disease. Such oxidative stress alters the redox sensitivity of the Kv2.1 delayed rectifier, resulting in the modulation of the channel.[8] In vitro studies and studies in animal models show that when KCNB1 is oxidized, it no longer conducts, leading to neurons becoming hyperpolarized and dying; oxidized KCNB1 also clusters in lipid rafts and cannot be internalized, which also leads to apoptosis. These alterations disrupt normal neuronal signaling and increase the likelihood of neurological diseases. Oxidized (oligomerized) KCNB1 channels are present in the hippocampi of old (Braak stage 1-2) and Alzheimer's disease (Braak stage 5) donors of either sexes [20][23]
As indicated earlier, oxidative and nitrosative injurious stimuli also activate a cell death-inducing cascade that promotes to a zinc and calcium/clamodulin-dependent interaction between syntaxin and Kv2.1, leading to the pro-apoptotic insertion of additional potassium channels into the plasma membrane. These new population of channels aid in the loss of intracellular potassium, creating a permissive environment for protease and nuclease activation in injured neurons.[8] Agents that interfere with the Kv2.1/syntaxin interaction are highly neuroprotective in acute ischemic injury models (stroke) [24]
Increased probability of the channel remaining open can also potentially drive neurodegeneration.
Cancer
Exploitation of this channel is advantageous in cancer cell survival as they have the ability to produce heme oxygenase-1, an enzyme with the ability to generate carbon monoxide (CO). Oncogenic cells benefit from producing CO due to the antagonizing effects of the KCNB1 channel. Inhibition of KCNB1 allows cancer proliferation without the apoptotic pathway preventing tumor formation. Although potassium channels are studied as a therapeutic target for cancer, this apoptotic regulation is dependent on cancer type, potassium channel type, expression levels, intracellular localization as well as regulation by pro- or anti-apoptotic factors.[26]
Interactions
KCNB1 has been shown to
See also
References
- ^ a b c GRCh38: Ensembl release 89: ENSG00000158445 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000050556 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ a b c "Entrez Gene: KCNB1 potassium voltage-gated channel, Shab-related subfamily, member 1".
- PMID 7774931.
- S2CID 219195192.
- ^ PMID 24323720.
- ^ a b c "Potassium channel, voltage-dependent, beta subunit, KCNAB1 (IPR005400)". InterPro. EMBL-EBI. Retrieved 2017-04-04.
- ^ S2CID 7990617.
- ^ PMID 26947620.
- ^ S2CID 37362059.
- PMID 27114846.
- PMID 10024359.
- PMID 23376354.
- S2CID 9830297.
- PMID 23275378.
- PMID 22442077.
- PMID 28383553.
- ^ PMID 30050035.
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- PMID 17206516.
- PMID 25333910.
- PMID 28483976.
- PMID 18459047.
- PMID 25450339.
- PMID 12060745.
- PMID 10921884.
Further reading
- Albrecht B, Lorra C, Stocker M, Pongs O (1994). "Cloning and characterization of a human delayed rectifier potassium channel gene". Receptors & Channels. 1 (2): 99–110. PMID 8081723.
- Hugnot JP, Salinas M, Lesage F, Guillemare E, de Weille J, Heurteaux C, Mattéi MG, Lazdunski M (July 1996). "Kv8.1, a new neuronal potassium channel subunit with specific inhibitory properties towards Shab and Shaw channels". The EMBO Journal. 15 (13): 3322–31. PMID 8670833.
- Post MA, Kirsch GE, Brown AM (December 1996). "Kv2.1 and electrically silent Kv6.1 potassium channel subunits combine and express a novel current". FEBS Letters. 399 (1–2): 177–82. S2CID 5691552.
- Patel AJ, Lazdunski M, Honoré E (November 1997). "Kv2.1/Kv9.3, a novel ATP-dependent delayed-rectifier K+ channel in oxygen-sensitive pulmonary artery myocytes". The EMBO Journal. 16 (22): 6615–25. PMID 9362476.
- Shepard AR, Rae JL (September 1999). "Electrically silent potassium channel subunits from human lens epithelium". The American Journal of Physiology. 277 (3 Pt 1): C412-24. PMID 10484328.
- Zhu XR, Netzer R, Böhlke K, Liu Q, Pongs O (1999). "Structural and functional characterization of Kv6.2 a new gamma-subunit of voltage-gated potassium channel". Receptors & Channels. 6 (5): 337–50. PMID 10551266.
- Sano Y, Mochizuki S, Miyake A, Kitada C, Inamura K, Yokoi H, Nozawa K, Matsushime H, Furuichi K (February 2002). "Molecular cloning and characterization of Kv6.3, a novel modulatory subunit for voltage-gated K(+) channel Kv2.1". FEBS Letters. 512 (1–3): 230–4. S2CID 83987133.
- Kurata HT, Soon GS, Eldstrom JR, Lu GW, Steele DF, Fedida D (August 2002). "Amino-terminal determinants of U-type inactivation of voltage-gated K+ channels". The Journal of Biological Chemistry. 277 (32): 29045–53. PMID 12021261.
- MacDonald PE, Wang G, Tsuk S, Dodo C, Kang Y, Tang L, Wheeler MB, Cattral MS, Lakey JR, Salapatek AM, Lotan I, Gaisano HY (November 2002). "Synaptosome-associated protein of 25 kilodaltons modulates Kv2.1 voltage-dependent K(+) channels in neuroendocrine islet beta-cells through an interaction with the channel N terminus". Molecular Endocrinology. 16 (11): 2452–61. PMID 12403834.
- Ju M, Stevens L, Leadbitter E, Wray D (April 2003). "The Roles of N- and C-terminal determinants in the activation of the Kv2.1 potassium channel". The Journal of Biological Chemistry. 278 (15): 12769–78. PMID 12560340.
- Tiran Z, Peretz A, Attali B, Elson A (May 2003). "Phosphorylation-dependent regulation of Kv2.1 Channel activity at tyrosine 124 by Src and by protein-tyrosine phosphatase epsilon". The Journal of Biological Chemistry. 278 (19): 17509–14. PMID 12615930.
- Consiglio JF, Korn SJ (April 2004). "Influence of permeant ions on voltage sensor function in the Kv2.1 potassium channel". The Journal of General Physiology. 123 (4): 387–400. PMID 15024041.
- Thébaud B, Michelakis ED, Wu XC, Moudgil R, Kuzyk M, Dyck JR, Harry G, Hashimoto K, Haromy A, Rebeyka I, Archer SL (September 2004). "Oxygen-sensitive Kv channel gene transfer confers oxygen responsiveness to preterm rabbit and remodeled human ductus arteriosus: implications for infants with patent ductus arteriosus". Circulation. 110 (11): 1372–9. PMID 15353504.
- Kerschensteiner D, Soto F, Stocker M (April 2005). "Fluorescence measurements reveal stoichiometry of K+ channels formed by modulatory and delayed rectifier alpha-subunits". Proceedings of the National Academy of Sciences of the United States of America. 102 (17): 6160–5. PMID 15827117.
External links
- Kv2.1+Potassium+Channel at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- KCNB1+protein,+human at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
This article incorporates text from the United States National Library of Medicine, which is in the public domain.