Functional Modularity of the β-Subunit of Voltage-Gated Ca2+ Channels

Abstract

The beta-subunit of voltage-gated Ca(2+) channels plays a dual role in chaperoning the channels to the plasma membrane and modulating their gating. It contains five distinct modular domains/regions, including the variable N- and C-terminus, a conserved Src homology 3 (SH3) domain, a conserved guanylate kinase (GK) domain, and a connecting variable and flexible HOOK region. Recent crystallographic studies revealed a highly conserved interaction between the GK domain and alpha interaction domain (AID), the high-affinity binding site in the pore-forming alpha(1) subunit. Here we show that the AID-GK domain interaction is necessary for beta-subunit-stimulated Ca(2+) channel surface expression and that the GK domain alone can carry out this function. We also examined the role of each region of all four beta-subunit subfamilies in modulating P/Q-type Ca(2+) channel gating and demonstrate that the beta-subunit functions modularly. Our results support a model that the conserved AID-GK domain interaction anchors the beta-subunit to the alpha(1) subunit, enabling alpha(1)-beta pair-specific low-affinity interactions involving the N-terminus and the HOOK region, which confer on each of the four beta-subunit subfamilies its distinctive modulatory properties.

Characterization of Cav1.4 Complexes (α11.4, β2, and α2δ4) in HEK293T Cells and in the Retina

“…1A), we predicted that these splice variants may have distinct effects on VDI of Ca v 1.4. Consistent with previous findings that the HOOK domain did not affect voltage-dependent activation (48), there were no differences in V h or k obtained from normalized tail current-voltage curves in cells transfected with Ca v 1.4 ␣ 1 -␤ 2X13 -␣ 2 ␦ 4 or Ca v 1.4 ␣ 1 -␤ 2a -␣ 2 ␦ 4 (Fig. 8, A and B, and Table 2).…”

“…The HOOK domains of ␤ 1b , ␤ 1c , ␤ 3 , and ␤ 4 are the same length as (and contain the same sequence (AKQKQK) that is present in) the ␤ 2X13 exon 7B (1). Transfer of the HOOK domain from ␤ 1b to ␤ 2a causes strong VDI of Ca v 2.1 channels, typical of ␤ 1b (48). Moreover, deletion of the HOOK domain from ␤ 2a enhances VDI of Ca v 2.2 channels (49).…”

“…There was no significant difference in (47). Structure/function analyses indicate that this property of ␤ 2a is mediated by the HOOK domain (48,49). Because ␤ 2X13 and ␤ 2a differ in the HOOK domain (Fig.…”

Three-Dimensional Localization of the α and β Subunits and of the II-III Loop in the Skeletal Muscle L-type Ca2+ Channel

“…6). 3D Location of the ␤ Subunit-Ca V ␤ subunits have hypervariable N-and C-termini that flank a core comprised of SH3, HOOK, and GK domains (52)(53)(54)(55). Several atomic structures for the core of different ␤ subunit isoforms obtained by x-ray crystallography (24 -26) present high structural similarity among them, with RMSD below 1 Å for all the pairs.…”

Direct inhibition of P/Q-type voltage-gated Ca 2+ channels by Gem does not require a direct Gem/Ca v β interaction

“…2 and 3). Both effects depend critically on the binding of Ca v β to the α interacting domain (AID) in the cytoplasmic loop (referred to as the I-II loop) connecting the first two homologous repeats of Ca v α 1 (2)(3)(4)(5)(6)(7)(8)(9)(10)(11). Gating regulation by Ca v β also needs a continuous α-helix between the AID and the S6 segment of the first repeat (IS6) of Ca v α 1 (3,8,9,12).…”