Calcineurin B (CLNB)

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Calcineurin B (CLNB) is the regulatory subunit and calcineurin A is the catalytic subunit of a protein phosphatase. Calmodulin also binds to calcineurin A; both CLNB and CAM in their calcium forms are required for catalytic activity. The crystal structure of Ca4-CLNB, complexed with an _-helical fragment (350-370) of calcineurin A and with the drug complex, FKBP12-FK506, [17, 18] shows both lobe 1,2 and lobe 3,4 embracing the fragment in their grooves homologous to those of CAM and TNC. In CLNB the two lobes bind to the same side of the target and are displaced about 22 _ along it. In contrast the two lobes of CAM enfold the target peptide from myosin light chain kinase on opposite sides and are related by an approximate two fold rotation axis. The seven subfamilies (CLNB, P22, VIS CALS, DREM, CMPK, and SOS3) are reasonably congruent (figure 6).