The β Subunit of the High Conductance Calcium-activated Potassium Channel

Hanner, Markus; Vianna‐Jorge, Rosane; Kamassah, Augustus; Schmalhofer, William A.; Knaus, Hans−Günther; Kaczorowski, Gregory J.; García, María L.

doi:10.1074/jbc.273.26.16289

Cited by 70 publications

(56 citation statements)

References 25 publications

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“…1A) in the other ␤ subunits as well. Four cysteines located in the extracellular domain that have been shown to form disulfide bridges (43) in ␤1 are conserved in all ␤ subunits (white on black C residues in Fig. 1A).…”

Section: Resultsmentioning

confidence: 99%

“…1A) has been shown to directly cross-link with charybdotoxin (45 Fig. 1A) are required for high affinity binding of charybdotoxin to the BK channel (43). All these residues are conserved in H␤1.…”

Section: Resultsmentioning

confidence: 99%

“…Putative transmembrane domains are shown boxed. White on black cysteine residues denote the four cysteines that are proposed to form disulfide bridges and are required for high affinity charybdotoxin binding (43) in the ␤1 subunit. The lysine residue in ␤1 subunits that cross-links with charybdotoxin (45) is circled and labeled above with "ChTX".…”

Section: Methodsmentioning

confidence: 99%

“…An N-linked glycosylation site that is conserved throughout the ␤ gene family is labeled with . Asterisks label ␤1 residues required for high affinity binding of charybdotoxin to Hslo1 channels (43). B, table of percent identity (value above) and percent conservation (similar plus identical residues, value below) between different human ␤ subunits.…”

Section: Methodsmentioning

confidence: 99%

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Cloning and Functional Characterization of Novel Large Conductance Calcium-activated Potassium Channel β Subunits, hKCNMB3 and hKCNMB4

Brenner¹,

Jegla²,

Wickenden³

et al. 2000

Journal of Biological Chemistry

446

589

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We present the cloning and characterization of two novel calcium-activated potassium channel ␤ subunits, hKCNMB3 and hKCNMB4, that are enriched in the testis and brain, respectively. We compare and contrast the steady state and kinetic properties of these ␤ subunits with the previously cloned mouse ␤1 (mKCNMB1) and the human ␤2 subunit (hKCNMB2). Once inactivation is removed, we find that hKCNMB2 has properties similar to mKCNMB1. hKCNMB2 slows Hslo1 channel gating and shifts the current-voltage relationship to more negative potentials. hKCNMB3 and hKCNMB4 have distinct effects on slo currents not observed with mKCNMB1 and hKCNMB2. Although we found that hKCNMB3 does interact with Hslo channels, its effects on Hslo1 channel properties were slight, increasing Hslo1 activation rates. In contrast, hKCNMB4 slows Hslo1 gating kinetics, and modulates the apparent calcium sensitivity of Hslo1. We found that the different effects of the ␤ subunits on some Hslo1 channel properties are calcium-dependent. mKCNMB1 and hKCNMB2 slow activation at 1 M but not at 10 M free calcium concentrations. hKC-NMB4 decreases Hslo1 channel openings at low calcium concentrations but increases channel openings at high calcium concentrations. These results suggest that ␤ subunits in diverse tissue types fine-tune slo channel properties to the needs of a particular cell.The large conductance calcium-activated potassium channel (BK) 1 is a unique member of the six transmembrane domain potassium channel family that is activated by voltage and calcium. BK channels are composed of a pore-forming ␣ subunit (1, 2) and, in some tissues, are tightly associated with an accessory ␤ subunit (3, 4). BK channels have diverse physiological properties with tissue-specific distribution. In neurons, BK channels are functionally colocalized with calcium channels (5, 6), shape action potential wave forms (7,8), and modulate neurotransmitter release (9, 10). In smooth muscle, BK channels regulate constriction in arteries (11), uterine contraction (12), and filtration rate in the kidney (13). Unlike other potassium channel families, BK channels can as yet only be attributed to a single gene, slowpoke (slo), that encodes the poreforming ␣ subunit of the channel. In light of the broad tissue localization and diverse functional properties, it is not surprising that a number of mechanisms have been identified that alter slo channel properties. These include alternative splicing of the slo RNA (14 -18), heteromeric assembly with other subunits (slak) (19), and modification by phosphorylation/dephosphorylation (20 -22) and oxidation/reduction (23).In addition, accessory ␤ subunits are a means of generating BK channel diversity. Coexpression of the ␤1 subunit in Xenopus oocytes increases the apparent calcium sensitivity, slows activation kinetics, and increases charybdotoxin binding affinity (24 -27). ␤1 subunit mRNA is enriched in smooth muscle (28) and can account for the apparent increased calcium sensitivity of BK channels in that tissue relative to skeletal muscl...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Cloning and Functional Characterization of Novel Large Conductance Calcium-activated Potassium Channel β Subunits, hKCNMB3 and hKCNMB4

Brenner¹,

Jegla²,

Wickenden³

et al. 2000

Journal of Biological Chemistry

446

589

View full text Add to dashboard Cite

show abstract

“…Therefore, they should be the easier sites to be approached by antibody. Moreover, the central part of the loop is usually considered to be difficult to approach because it lays over the channel pore and deep into the cell surface (30,31). According to the above rule of accessibility, the structural profile of the extracellualr loop can be depicted in a letter "M," of which the valley is around the middle too.…”

Section: Accessibility Of the Extracellular Segment Of H␤2 For Antibomentioning

confidence: 99%

Four-turn α-Helical Segment Prevents Surface Expression of the Auxiliary hβ2 Subunit of BK-type Channel

Chen

Gan

et al. 2008

Journal of Biological Chemistry

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Large conductance, voltage-and Ca 2؉ -activated K ؉ (BK) channels encoded by the mslo ␣ and ␤2 subunits exist abundantly in rat chromaffin cells, pancreatic ␤ cells, and DRG neurons. The extracellular loop of h␤2 acting as the channel regulator influences the rectification and toxin sensitivity of BK channels, and the inactivation domain at its N terminus induces rapid inactivation. However, the regulatory mechanism, especially the trafficking mechanism of h␤2, is still unknown. With the help of immunofluorescence and patch clamp techniques, we determine that the h␤2 subunit alone resides in the endoplasmic reticulum, suggesting that trafficking mechanism of h␤2 differs from that of h␤1 opposite to what we predicted previously. We further demonstrate that a four-turn ␣ helical segment at the N terminus of h␤2 prevents the surface expression of h␤2, that is, the helical segment itself is a retention signal. Using the c-Myc epitope-tagged extracellular loop of h␤2, we reveal that the most accessible site by antibody is located at the middle of the extracellular loop, which might provide clues to understand how the auxiliary ␤ subunits regulates the toxin sensitivity and the rectification of BK-type channels.Large conductance voltage-and Ca 2ϩ -activated K ϩ (BK) 4 channels associated with its auxiliary ␤ subunits show functional varieties in many native cells (1-13). The auxiliary ␤1-␤4 subunits of BK channels are composed of two transmembrane segments and a large extracellular segment (5, 14 -16). For h␤2 subunits, three hydrophobic residues FIW at its N terminus produces a rapid inactivation of BK channels (15), whereas it does not follow a typical N-type inactivation mechanism (17). The NMR experiment reveals a four-turn helix structure located at the middle of its N terminus (24). Recently, Zhang et al. (18) reported that trypsin can easily target the Arg 8 and Arg 9 of nine basic residues before the helix. In addition, its extracellular loop prevents the scorpion toxin charybdotoxin from approaching the channel pore (9) and induces the rectification of BK channels (19). It has been reported that the ␤1 and ␤2 subunits contain endocytic sorting signals at their C termini, which can down-regulate the association MaxiK channel surface expression levels (14, 20). The ␤1 subunit can reach the cell membrane alone, whereas the ␤2 subunit only appears underneath the plasma membrane (14,20,21). Obviously, the trafficking mechanism of h␤2 subunits is still unknown so far. There are many mechanisms for governing the surface expression of ion channels and thus the electrical activity of a cell. A channel protein in a misfolded or unfolded state can be trapped in the ER as demonstrated by measurements of the surface labeling, luminomitry. Some retrieval/retention and anterograde signals determine the ER exit of proteins (22). The retention sequence RKR appearing in potassium inward rectifying channel (Kir) and its auxiliary SUR1 subunit is due to improperly folded or assembled channels (22,23). Both the Kir and SUR1 sub...

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Development of charybdotoxin Q18F variant as a selective peptide blocker of neuronal BK(α + β4) channel for the treatment of epileptic seizures

et al. 2022

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Epilepsy is the results from the imbalance between inhibition and excitation in neural circuits, which is mainly treated by some chemical drugs with side effects. Gain‐of‐function of BK channels or knockout of its β4 subunit associates with spontaneous epilepsy. Currently, few reports were published about the efficacy of BK(α + β4) channel modulators in epilepsy prevention. Charybdotoxin is a non‐specific inhibitor of BK and other K+ channels. Here, by nuclear magnetic resonance (NMR) and other biochemical techniques, we found that charybdotoxin might interact with the extracellular loop of human β4 subunit (i.e., hβ4‐loop) of BK(α + β4) channel at a molar ratio 4:1 (hβ4‐loop vs. charybdotoxin). Charybdotoxin enhanced its ability to prevent K+ current of BK(α + β4 H101Y) channel. The charybdotoxin Q18F variant selectively reduced the neuronal spiking frequency and increased interspike intervals of BK(α + β4) channel by π–π stacking interactions between its residue Phe18 and residue His101 of hβ4‐loop. Moreover, intrahippocampal infusion of charybdotoxin Q18F variant significantly increased latency time of seizure, reduced seizure duration and seizure numbers on pentylenetetrazole‐induced pre‐sensitized rats, inhibited hippocampal hyperexcitability and c‐Fos expression, and displayed neuroprotective effects on hippocampal neurons. These results implied that charybdotoxin Q18F variant could be potentially used for intractable epilepsy treatment by therapeutically targeting BK(α + β4) channel.

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The β Subunit of the High Conductance Calcium-activated Potassium Channel

Cited by 70 publications

References 25 publications

Cloning and Functional Characterization of Novel Large Conductance Calcium-activated Potassium Channel β Subunits, hKCNMB3 and hKCNMB4

Cloning and Functional Characterization of Novel Large Conductance Calcium-activated Potassium Channel β Subunits, hKCNMB3 and hKCNMB4

Four-turn α-Helical Segment Prevents Surface Expression of the Auxiliary hβ2 Subunit of BK-type Channel

Development of charybdotoxin Q18F variant as a selective peptide blocker of neuronal BK(α + β4) channel for the treatment of epileptic seizures

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