Bestrophin-4 is a 473 amino acid member of the Bestrophin family of proteins. Members of the Bestrophin family are transmembrane proteins that contain a high percentage of aromatic residues, a conserved RFP (Arg-Phe-Pro) motif and they function as anion channels. Bestrophin-4 acts as a calcium-sensitive chloride channel located in the cell membrane. It is believed that Bestrophin-4 also acts as a channel for other physiologically significant anions, such as bicarbonate. Bestrophin-4 is predominantly expressed in the colon, but can be found at low levels in testis, placenta, trachea, spinal chord, lung and retina.