Association of β-catenin with the α-subunit of neuronal large-conductance Ca ²⁺ -activated K+ channels

Abstract

, and neurons contributes to rapid repolarization of the membrane after excitation. Ca 2؉ channels have been shown to bind to a large set of synaptic proteins, but the proteins interacting with Ca 2؉ -activated K ؉ channels remain unknown. Here, we report that the large-conductance Ca 2؉ -activated K ؉ channel of the chicken's cochlear hair cell interacts with ␤-catenin. Yeast two-hybrid assays identified the S10 region of the K ؉ channel's ␣-subunit and the ninth armadillo repeat and carboxyl terminus of ␤-catenin as necessary for the interaction. An antiserum directed against the ␣-subunit specifically coprecipitated ␤-catenin from brain synaptic proteins. ␤-Catenin is known to associate with the synaptic protein Lin7͞Velis͞MALS, whose interaction partner Lin2͞CASK also binds voltage-gated Ca 2؉ channels. ␤-Catenin may therefore provide a physical link between the two types of channels at the presynaptic active zone.T he hair cell, the sensory receptor of the internal ear, releases neurotransmitter at presynaptic active zones studding its basolateral membrane surface (for a review, see ref. 1). Examination of hair cells by loose-seal patch recording demonstrated that each active zone bears a cluster of voltage-gated Ca 2ϩ (Ca V ) channels and Ca 2ϩ -activated K ϩ (K Ca ) channels (2-4). When Ca V channels are activated by a hair cell's depolarization in response to acoustical stimulation, the resultant Ca 2ϩ influx not only triggers synaptic-vesicle release but also opens K Ca channels. The efflux of K ϩ through these channels causes a rapid repolarization that plays a key role in the electrical oscillation that tunes some hair cells (5) and in fast inhibitory synaptic transmission (6). Nerve terminals of the central and peripheral nervous system, including those at the neuromuscular junction, use a similar mechanism to effect repolarization in anticipation of the next action potential (7-11). The presynaptic colocalization of K Ca channels with Ca V channels is thus indispensable for normal electrical signaling by excitatory cells.Electrophysiological and molecular-biological analyses have shown that hair cells express L-type Ca V channels and largeconductance (BK or Maxi) K Ca channels (12-15) that contain, respectively, ␣ 1D -subunits (16-18) and slowpoke (slo) ␣-and slo ␤-subunits (19-22). In hippocampal neurons, both large-and small-conductance K ϩ channels occur in presynaptic regions and are associated, respectively, with L-and N-type Ca V channels (7, 23). The Ca V channels at the presynaptic active zone form a protein complex with several anchoring proteins (24-26), such as Mint-1, CASK, and Rab3-interacting molecule (RIM) binding proteins (RBP). In Drosophila, two cytosolic regulatory proteins, Slob and dSLIP, and two protein kinases, Src and PKAc, are able to assemble with the slo ␣-subunit (27-29). In vertebrates, however, only kinases, such as Src and Syk, have been reported to interact with this subunit (30-32). To seek other proteins that associate with K Ca channels and mediate their presynapti...

A Protein Interaction Network for the Large Conductance Ca2+-activated K+ Channel in the Mouse Cochlea

“…Its relation to Ca 2ϩ channels in the cochlea likely lies in its interaction with ␤-catenin. The BKAP ␤-catenin was identified using BK as bait in a Y2H screening of a cochlea library (44). This study suggests that ␤-catenin may organize BK at these sites based on previous evidence.…”

Coassembly of Big Conductance Ca2+-activated K+ Channels and L-type Voltage-gated Ca2+ Channels in Rat Brain

“…A direct interaction among the two ion channel proteins might be expected, but, more likely, a number of yet unidentified accessory proteins could be present. Such scaffolding proteins have been demonstrated for a number of other proteins functionally linked in the plasma membrane (34).…”

Nanodomains of Single Ca2+Channels Contribute to Action Potential Repolarization in Cortical Neurons

“…However, because the physical extent of an ion channel protein is ϳ8 nm (Hille, 1992), the range of possible distances between individual BK and Ca 2ϩ channels that yields an average of 13 nm has to be ϳ8 -18 nm (assuming a symmetrical distribution). Such a constant spacing is suggestive of a physical link between the two channels that could potentially be mediated by ␤-catenin (Lesage et al, 2004).…”