A novel calcium channel Cavβ2 splice variant with unique properties predominates in the retina

Abstract

Cavβ subunits are essential for surface expression of voltage-gated calcium channel complexes and crucially modulate biophysical properties like voltage-dependent inactivation. Here, we describe the discovery and characterization of a novel Cavβ₂ variant with distinct features that predominates in the retina. We determined spliced exons in retinal transcripts of the Cacnb2 gene, coding for Cavβ₂, by RNA-Seq data analysis and quantitative PCR. We cloned a novel Cavβ₂ splice variant from mouse retina, which we are calling β_2i, and investigated biophysical properties of calcium currents with this variant in a heterologous expression system as well as its intrinsic membrane interaction when expressed alone. Our data showed that β_2i predominated in the retina with expression in photoreceptors and bipolar cells. Furthermore, we observed that the β_2i N-terminus exhibited an extraordinary concentration of hydrophobic residues, a distinct feature not seen in canonical variants. The biophysical properties resembled known membrane-associated variants, and β_2i exhibited both a strong membrane association and a propensity for clustering, which depended on hydrophobic residues in its N-terminus. We considered available Cavβ structure data to elucidate potential mechanisms underlying the observed characteristics but resolved N-terminus structures were lacking and thus, precluded clear conclusions. With this description of a novel N-terminus variant of Cavβ₂, we expand the scope of functional variation through N-terminal splicing with a distinct form of membrane attachment. Further investigation of the molecular mechanisms underlying the features of β_2i could provide new angles on the way Cavβ subunits modulate Ca²⁺ channels at the plasma membrane.

Keywords: alternative splicing; biophysics; calcium channel; photoreceptor; physiology; retina.