Channelpedia

cacnb1

Description: calcium channel, voltage-dependent, beta 1 subunit
Gene: Cacnb1     Synonyms: cacnb1, CAB1, CACNLB1, CCHLB1

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Introduction

CACNB1 (also known as CAB1; CCHLB1; CACNLB1; MGC41896) encodes a calcium channel beta subunit. It plays an important role in the calcium channel by modulating G protein inhibition, increasing peak calcium current, controlling the alpha-1 subunit membrane targeting and shifting the voltage dependence of activation and inactivation. Alternative splicing occurs at this locus and three transcript variants encoding three distinct isoforms have been identified.

http://www.ncbi.nlm.nih.gov/gene/782


Experimental data


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Gene

RGD ID Chromosome Position Species
68382 10 86764283-86784791 Rat
68553 11 97864215-97883941 Mouse
68552 17 37329709-37353901 Human

Cacnb1 : calcium channel, voltage-dependent, beta 1 subunit


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Transcript

Acc No Sequence Length Source
NM_017346 n/A n/A NCBI
NM_031173 n/A n/A NCBI
NM_001159319 n/A n/A NCBI
NM_001159320 n/A n/A NCBI
NM_145121 n/A n/A NCBI
NM_199248 n/A n/A NCBI
NM_199247 n/A n/A NCBI
NM_000723 n/A n/A NCBI

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Ontology

Accession Name Definition Evidence
GO:0005891 voltage-gated calcium channel complex A protein complex that forms a transmembrane channel through which calcium ions may pass in response to changes in membrane potential. IDA
GO:0042383 sarcolemma The outer membrane of a muscle cell, consisting of the plasma membrane, a covering basement membrane (about 100 nm thick and sometimes common to more than one fiber), and the associated loose network of collagen fibers. IEA

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Interaction


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Protein


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Structure

CaV1.1 is a large transmembrane protein which contains both the Ca2+ conducting pore and the voltage sensing S4 domain. Four other auxiliary subunits bind CaV1.1 to make up DHPR (dihydropyridine receptor, that serves as a modest L-type Ca2+ channel but is primarily known for its function as a voltage sensor. For review, see Flucher et al. 2005 [1253]), with the most widely studied being the cytosolic CaVβ1a (cacnb1) subunit. CaVβ1a, a muscle specific member of the CaVβ family of proteins, binds to a region of the I–II intracellular loop of CaV1.1 known as the alpha interaction domain (AID) (Chen et al. 2004 [1254]). The correct organization of CaV1.1 into tetrads within the t-tubule membrane is a specific function of the CaVβ1a isoform (Schredelseker et al. 2005 [1255]).


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Distribution


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Expression

The b1a subunit is one of the auxiliary subunits of CaV1.1 channels (Isom et al. 1994 [1247] and see Channelpedia entry of Cav1.1) and the main isoform among the b1 subunits present in muscle (Ren & Hall, 1997 [1248]).

CaVβ1a expression is highly increased in old mice (Taylor [1249]).


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Functional

The b1a subunit has important effects on the surface expression of alpha-1 subunits, e.g. Cav1.1. cacnb1 subunit produces major changes in the amplitude of L-type currents without any effect on charge movement. (García [234])

Although classically known for augmenting the expression and function of CaV1 subfamily of calcium channels, the CaVβ family of subunits may contribute to the down-regulation of CaV1 as well (Taylor et al. [1249]). A family of Ras-related G-proteins (RGKs) mediate the down-regulation of several CaV1 isoforms in a CaVβ dependent manner (Beguin et al. 2001 [504]). Additionally, the previously uncharacterized SH3 domain of CaVβ was shown to bind dynamin and mediate endocytosis of CaV1.2 (Gonzalez-Gutierrez et al. 2007 [1256]).

CaVβ1a is classically described by its role in chaperoning CaV1.1 to the plasma membrane and regulating L-type Ca2+ current (Gregg et al. 1996 [1257]; Strube et al. 1996 [1258]; Beurg et al. 1997 [1259]; Neuhuber et al. 1998 [1260]). Most notably, excitation-contraction (E-C) coupling cannot occur without CaVβ1a (Gregg et al. 1996 [1257]). CaVβ1a binds to charged residues on RyR (Cheng et al. 2005 [1254]) and neutralization of these residues reduces E-C coupling, suggesting a direct interaction with ryanodine receptor (RyR). The correct organization of CaV1.1 into tetrads within the t-tubule membrane is also a specific function of the CaVβ1a isoform (Schredelseker et al. 2005 [1255]).

Experimental overexpression of CaVβ1a reduces both the expression of CaV1.1 and specific force in dissociated single fibers of young mice. Additionally, siRNA inhibition of CaVβ1a restores charge movement in aged muscle. These findings suggest that overexpression of CaVβ1a with aging contributes to excitation-contraction uncoupling by reducing the level of CaV1.1. (Taylor [1249])


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Kinetics


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Model


References

Catterall WA. et al. Auxiliary subunits of voltage-gated ion channels.
Neuron, 1994 Jun , 12 (1183-94).

1250

Xie D. et al. Subunits of voltage-gated calcium channels in murine spiral ganglion cells.
Acta Otolaryngol., 2007 Jan , 127 (8-12).

Tuluc P. et al. The role of auxiliary dihydropyridine receptor subunits in muscle.
J. Muscle Res. Cell. Motil., 2005 , 26 (1-6).

Obermair GJ. et al. The beta 1a subunit is essential for the assembly of dihydropyridine-receptor arrays in skeletal muscle.
Proc. Natl. Acad. Sci. U.S.A., 2005 Nov 22 , 102 (17219-24).


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