BARP suppresses voltage-gated calcium channel activity and Ca2+-evoked exocytosis

Voltage-gated calcium channels (VGCCs) are key regulators of cell signaling and Ca²⁺-dependent release of neurotransmitters and hormones. Understanding the mechanisms that inactivate VGCCs to prevent intracellular Ca²⁺ overload and govern their specific subcellular localization is of critical importance. We report the identification and functional characterization of VGCC β-anchoring and -regulatory protein (BARP), a previously uncharacterized integral membrane glycoprotein expressed in neuroendocrine cells and neurons. BARP interacts via two cytosolic domains (I and II) with all Ca_vβ subunit isoforms, affecting their subcellular localization and suppressing VGCC activity. Domain I interacts at the α₁ interaction domain–binding pocket in Ca_vβ and interferes with the association between Ca_vβ and Ca_vα1. In the absence of domain I binding, BARP can form a ternary complex with Ca_vα1 and Ca_vβ via domain II. BARP does not affect cell surface expression of Ca_vα1 but inhibits Ca²⁺ channel activity at the plasma membrane, resulting in the inhibition of Ca²⁺-evoked exocytosis. Thus, BARP can modulate the localization of Ca_vβ and its association with the Ca_vα1 subunit to negatively regulate VGCC activity.