The β3 protein is an auxiliary subunit of the Ca_V (voltage-dependent calcium) channel multimer complex. Four β isoforms were identified in mammalian genomes and they share some sequence as well as structure homology.^1-3  The structure of Ca_Vβ3 was recently determined (as well as other Ca_Vβ subunits; for review see reference 3). Ca_Vβ subunits are cytoplasmic proteins, that bind the cytoplasmic face of the pore forming Ca_V α1 subunits. These interactions have profound effects on channel trafficking to the plasma membrane as well as on current parameters such as voltage-dependent kinetics and interactions with modulatory proteins.^1,2  Ca_Vβ3 might interact with all the pore-forming subunits that have been tested and in vivo is expressed in smooth muscle, trachea, aorta, lung and brain.¹