Background：Protein phosphatase 3 (PPP3, formerly PP2B, Calcineurin), a serine/ threonine protein phosphatase, is a heterodimer composed of one catalytic subunit (PPP3C, Calcineurin A) and one regulatory subunit (PPP3R, Calcineurin B). PPP3R has two isoforms, PPP3R1 and PPP3R2. PPP3Rl is ubiquitously expressed in different tissues and is coded by the PPP3R1 gene which was mapped recently to human chromosome 2. PPP3Rl has four functional calcium-binding sites.
