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Characterization of the calcium‐binding sites of calcineurin B
Author(s) -
Kakalis Lazaros T,
Kennedy Michael,
Sikkink Robert,
Rusnak Frank,
Armitage Ian M
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)00207-p
Subject(s) - chemistry , calcineurin , fkbp , calcium , calmodulin , binding site , serine , pentagonal bipyramidal molecular geometry , dephosphorylation , ef hand , protein subunit , biochemistry , stereochemistry , phosphatase , phosphorylation , crystallography , crystal structure , medicine , surgery , organic chemistry , transplantation , gene
Calcineurin (CaN) is a calcium‐ and calmodulin‐dependent serine/threonine phosphatase whose inhibition by the immunosuppressant‐immunophilin complexes (cyclosporin‐cyclophilin and FK506‐FKBP) is considered key to the mechanism of immunosuppression. CaN is a heterodimer, consisting of a 59 kDa catalytic subunit (A) and a 19 kDa calcium‐binding regulatory subunit (B). The latter is postulated to harbor four calcium binding domains of the EF hand type. The titration of the CaN B apoprotein with the isomorphic Cd 2+ was followed by 113 Cd NMR and these data support one high‐affinity metal binding site and three lower‐affinity ones. Flow dialysis data with Ca 2+ indicate one high affinity calcium binding site with K d ∼ 2.4 × 10 −8 M and three other sites with K d ∼ 1.5 × 10 −5 M. The chemical shifts of all four 113 Cd resonances (−75, −93, −106 and −119 ppm) are in the same range as found in other 113 Cd substituted calcium‐binding proteins, and are indicative of all‐oxygen coordination of pentagonal bipyramidal geometry.