Calcium Binding Protein P22 (CHP)

Calcium binding protein P22 is a phosphoprotein that binds to the sodium-potassium exchangers (NHEs). This protein serves as an essential cofactor which supports the physiological activity of NHE family members. It has protein sequence similarity to calcineurin B and it is also known to be an endogenous inhibitor of calcineurin activity.

A partial sequence obtained from this screen was used to clone a novel full-length cDNA, designated CHP, from a second B-cell library. The deduced 195-amino acid protein contains 2 distinct and 2 potential EF-hand Ca(2+)-binding motifs and shares 43% and 33% identity with calcineurin B and calmodulin, respectively. It also shares 99% sequence identity with the rat homolog. Northern blot analysis demonstrated expression of a 4-kb CHP transcript in all 8 fetal tissues examined.