Structural basis of the α1–β subunit interaction of voltage-gated Ca2+ channels

Abstract

High-voltage-activated Ca2+ channels are essential for diverse biological processes. They are composed of four or five subunits, including alpha1, alpha2-delta, beta and gamma (ref. 1). Their expression and function are critically dependent on the beta-subunit, which transports alpha1 to the surface membrane and regulates diverse channel properties. It is believed that the beta-subunit interacts with alpha1 primarily through the beta-interaction domain (BID), which binds directly to the alpha-interaction domain (AID) of alpha1; however, the molecular mechanism of the alpha1-beta interaction is largely unclear. Here we report the crystal structures of the conserved core region of beta3, alone and in complex with AID, and of beta4 alone. The structures show that the beta-subunit core contains two interacting domains: a Src homology 3 (SH3) domain and a guanylate kinase (GK) domain. The AID binds to a hydrophobic groove in the GK domain through extensive interactions, conferring extremely high affinity between alpha1 and beta-subunits. The BID is essential both for the structural integrity of and for bridging the SH3 and GK domains, but it does not participate directly in binding alpha1. The presence of multiple protein-interacting modules in the beta-subunit opens a new dimension to its function as a multi-functional protein.

The RGK family of GTP-binding proteins: Regulators of voltage-dependent calcium channels and cytoskeleton remodeling

“…All Ca V β subunits share a conserved domain structure with three variable regions separated by conserved SH3-like and GK-like domains [77]. The Ca V α interaction site is located within the GK domain of all Ca V β subunits and supports high affinity (low nanomolar) association with a conserved domain (termed the AID) of the α-subunits [77][78][79]. As first shown with Rem [71], and subsequently with the remainder of the RGK GTPases [18], deletion mapping studies have located the RGK binding domain to a region within the larger GK domain of Ca V β.…”

Uncoupling of Calcium Channel α1 and β Subunits in Developing Neurons

“…Together with work in rat hippocampal neurons (46), this suggested that membrane-associated guanylate kinase scaffolding proteins with PDZ, SH3, and guanylate kinase domains such as CASK are likely involved in targeting and stabilizing Ca v 2 calcium channels to synaptic contacts. It is interesting to note that calcium channel ␤ subunits also contain membrane-associated guanylate kinase-like SH3 and guanylate kinase domains (33)(34)(35), raising the possibility that secondary interactions of ␤ subunits with scaffolding proteins may aid in stabilizing and anchoring of LCa v 2 calcium channels in synaptic terminals.…”

“…1, A and C). Residues in the guanylate kinase domain contribute to form a deep, hydrophobic groove for high affinity binding of high voltage-activated calcium channels (33,35), which are highly conserved residues among invertebrate and mammalian ␤ subunits (Fig. 1A, black residues).…”

“…1, A and C). The ␤ subunit core is considered to resemble central modules of membrane-associated guanylate kinase homologs (33)(34)(35), with conserved and interacting SH3 and guanylate kinase domains, and a variable HOOK region that splits the SH3 fold (Fig. 1, A and C).…”

Voltage-Gated Calcium Channels

“…The three-dimensional structure of the Ca V b subunits has been determined at high resolution by X-ray crystallography (Fig. 3B) (Chen et al 2004;Van Petegem et al 2004). These subunits contain conserved SH3 and guanylate kinase domains like the MAGUK family of scaffolding proteins.…”