The beta subunit of voltage gated calcium channels is coded for by four genes 1-4. Gene 4 can produce two types of beta4A domain (beta4Aa and beta4Ab) according to how the gene splicing is carried out. This family is part of the beta4Aa N terminal domain. It is made up of an alpha helix and a beta strand. It is thought to regulate the channel properties through protein-protein interactions with non Ca channel proteins. [1]

1: Solution structure of the N-terminal A domain of the human voltage-gated Ca2+channel beta4a subunit. Vendel AC, Rithner CD, Lyons BA, Horne WA; Protein Sci. 2006;15:378-383. PMID:16385006