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1.A.1.3.2
Large conductance Ca2+ - and voltage-activated K+ channel, α-subunit (subunit α1), BK, BKCa, Kca1.1, Slowpoke, Slo1, KCNMA1 or MaxiK (functions with four β-subunits (TC# 8.A.14) encoded by genes KCNMB1-4 and the γ subunit (TC# 8.A.43) in humans (Toro et al. 2013; Li et al. 2016); the positions of beta2 and beta3 have been determined (Wu et al. 2013).  The KB channel is inhibited by 3 scorpion toxins, charybda toxin, iberiotoxin and slotoxin.  It forms a ''Ca2+  nanodomain'' complex with Cav1.2 (L-type; 1.A.1.11.4), Cav2.1 (P/Q-type; 1.A.1.11.5) and Cav2.2 (N-type; 1.A.1.11.6) where Ca2+ influx through the Cav channel activates BKCa (Berkefeld et al., 2006; Romanenko et al., 2006). The RCK2 domain is a Ca2+ sensor (Yusifov et al., 2008). Binding of Ca2+ to D367 and E535 changes the conformation around the binding site and turns the side chain of M513 into a hydrophobic core, explaining how Ca2+ binding opens the activation gate of the channel (Zhang et al., 2010). A structural motif in the C-terminal tail of Slo1 confers carbon monoxide sensitivity to human BKCa channels (Williams et al., 2008; Hou et al., 2008). These channels are present in the inner mitochondrial membrane of rat brain (Douglas et al., 2006).The Stress-Axis Regulated Exon (STREX) is responsible for stretch sensitivity. Ca2+ binds to two sites. Ca2+ binding to the RCK1 site is voltage dependent, but Ca2+ binding to the Ca2+ bowl is not (Sweet and Cox et al., 2008). Type 1 IP3 receptors activate BKCa channels via local molecular coupling in arterial smooth muscle cells (Zhao et al., 2010). The open structure is known (Yuan et al., 2012). BKCa is essential for ER calcium uptake in neurons and cardiomyocytes (Kuum et al., 2012) and link Ca2+ signaling to action potential firing and neurotransmitter release via serotonin receptors in many types of neurons (Rothberg 2012). The molecular mechanism of pharmacological activation of BK channels has been discussed by Gessner et al. (2012). The first TMS of the β2-subunit binds to TMS S1 of the α-subunit (Morera et al., 2012).  Mutations in Cav1.2 give rise to Timothy syndrome (Dixon et al. 2012).  Exhibits low voltage activation by interaction with Cav3 (Rehak et al. 2013) as well as Ca2+-gating (Berkefeld and Fakler 2013). Single-channel kinetics have been reported (Geng and Magleby 2014). The γ-subunit has TC# 8.A.43.1.8.  RBK channels regulate myogenesis in vascular smooth muscle cells (Krishnamoorthy-Natarajan and Koide 2016). Latorre et al. 2017 reviewed molecular, physiological and pathological aspects of Slo1. The microRNA, mmumiR449a, reduced the mRNA expression levels of transient receptor potential cation channel subfamily A member 1 (TRPA1), and calcium activated potassium channel subunit alpha1 (KCNMA1) and increased the level of transmembrane phosphatase with tension homology (TPTE) in the DRG cells (Lu et al. 2017), thereby reducing pain. The N-terminal sequence determines its modification by β-subunits (Lorca et al. 2017).

Accession Number:Q62976
Protein Name:Calcium-activated potassium channel subunit alpha-1
Length:1209
Molecular Weight:134374.00
Species: [10116]
Number of TMSs:7
Location1 / Topology2 / Orientation3: Endoplasmic reticulum membrane1 / Multi-pass membrane protein2
Substrate Ca+, K+

Cross database links:

Genevestigator: Q62976
RefSeq: NP_114016.1   
Entrez Gene ID: 83731   
Pfam: PF03493    PF00520    PF02254   
KEGG: rno:83731   

Gene Ontology

GO:0005789 C:endoplasmic reticulum membrane
GO:0048471 C:perinuclear region of cytoplasm
GO:0048787 C:presynaptic active zone membrane
GO:0008076 C:voltage-gated potassium channel complex
GO:0015269 F:calcium-activated potassium channel activity
GO:0003824 F:catalytic activity
GO:0046872 F:metal ion binding
GO:0005515 F:protein binding
GO:0005249 F:voltage-gated potassium channel activity
GO:0008152 P:metabolic process
GO:0006813 P:potassium ion transport
GO:0042312 P:regulation of vasodilation
GO:0051592 P:response to calcium ion
GO:0031960 P:response to corticosteroid stimulus
GO:0043627 P:response to estrogen stimulus
GO:0001666 P:response to hypoxia
GO:0009268 P:response to pH
GO:0055085 P:transmembrane transport

References (5)

[1] “Increased expression of Ca2+-sensitive K+ channels in aorta of hypertensive rats.”  Liu Y.et.al.   9403560
[2] “Functional characteristics of two BKCa channel variants differentially expressed in rat brain tissues.”  Ha T.S.et.al.   10651830
[3] “Identification and localization of Ca(2+)-activated K+ channels in rat sciatic nerve.”  Mi H.et.al.   10384881
[4] “Heme is a carbon monoxide receptor for large-conductance Ca2+-activated K+ channels.”  Jaggar J.H.et.al.   16166559
[5] “A novel MaxiK splice variant exhibits dominant-negative properties for surface expression.”  Zarei M.M.et.al.   11278440

External Searches:

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  • 2° Structure (Network Protein Sequence Analysis)

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Predict TMSs (Predict number of transmembrane segments)
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FASTA formatted sequence
1:	MANGGGGGGG GSSGSSGGGG GGGGGETALR MSSNIHANHL SLDASSSSSS SSSSSSSSSS 
61:	SVHEPKMDAL IIPVTMEVPC DSRGQRMWWA FLASSMVTFF GGLFIILLWR TLKYLWTVCC 
121:	HCGGKTKEAQ KINNGSSQAD GTLKPVDEKE EVVAAEVGWM TSVKDWAGVM ISAQTLTGRV 
181:	LVVLVFALSI GALVIYFIDS SNPIESCQNF YKDFTLQIDM AFNVFFLLYF GLRFIAANDK 
241:	LWFWLEVNSV VDFFTVPPVF VSVYLNRSWL GLRFLRALRL IQFSEILQFL NILKTSNSIK 
301:	LVNLLSIFIS TWLTAAGFIH LVENSGDPWE NFQNNQALTY WECVYLLMVT MSTVGYGDVY 
361:	AKTTLGRLFM VFFILGGLAM FASYVPEIIE LIGNRKKYGG SYSAVSGRKH IVVCGHITLE 
421:	SVSNFLKDFL HKDRDDVNVE IVFLHNISPN LELEALFKRH FTQVEFYQGS VLNPHDLARV 
481:	KIESADACLI LANKYCADPD AEDASNIMRV ISIKNYHPKI RIITQMLQYH NKAHLLNIPS 
541:	WNWKEGDDAI CLAELKLGFI AQSCLAQGLS TMLANLFSMR SFIKIEEDTW QKYYLEGVSN 
601:	EMYTEYLSSA FVGLSFPTVC ELCFVKLKLL MIAIEYKSAN RESRSRKRIL INPGNHLKIQ 
661:	EGTLGFFIAS DAKEVKRAFF YCKACHDDVT DPKRIKKCGC RRLEDEQPPT LSPKKKQRNG 
721:	GMRNSPNTSP KLMRHDPLLI PGNDQIDNMD SNVKKYDSTG MFHWCAPKEI EKVILTRSEA 
781:	AMTVLSGHVV VCIFGDVSSA LIGLRNLVMP LRASNFHYHE LKHIVFVGSI EYLKREWETL 
841:	HNFPKVSILP GTPLSRADLR AVNINLCDMC VILSANQNNI DDTSLQDKEC ILASLNIKSM 
901:	QFDDSIGVLQ ANSQGFTPPG MDRSSPDNSP VHGMLRQPSI TTGVNIPIIT ELAKPGKLPL 
961:	VSVNQEKNSG THILMITELV NDTNVQFLDQ DDDDDPDTEL YLTQPFACGT AFAVSVLDSL 
1021:	MSATYFNDNI LTLIRTLVTG GATPELEALI AEENALRGGY STPQTLANRD RCRVAQLALL 
1081:	DGPFADLGDG GCYGDLFCKA LKTYNMLCFG IYRLRDAHLS TPSQCTKRYV ITNPPYEFEL 
1141:	VPTDLIFCLM QFDHNAGQSR ASLSHSSHSS QSSSKKSSSV HSIPSTANRP NRPKSRESRD 
1201:	KQKKEMVYR