Calcineurin B- and calmodulin-binding preferences identified with phage-displayed peptide libraries

Calcineurin B (CnB) and calmodulin (CaM) are two structurally similar but f unctionally distinct 'EF-hand' Ca2+-binding proteins. CnB is the regulatory subunit of the CaM-stimulated protein phosphatase, calcineurin. CaM is a u nique multifunctional protein that interacts with and modulates the activit y of many target proteins. CnB and CaM are both required for the full activ ation of the phosphatase activity of calcineurin and are not interchangeabl e. The two proteins recognize distinct binding sites on calcineurin A subun it (CnA) and perform different functions. Phage-displayed peptide libraries (pIII and pVIII libraries) were screened with CnB and CaM to isolate pepti des that could then be compared to determine if there were binding preferen ces of the two proteins. The Ca2+-dependent binding of phage-displayed pept ides to CnB and CaM is specifically blocked by synthetic peptides derived f rom the CnB-binding domain of CnA and the CaM-binding domain of myosin ligh t chain kinase respectively. Both CnB- and CaM-binding peptides have a high content of tryptophan and leucine, but CnB-binding peptides are more hydro phobic than CaM-binding peptides. CnB-binding peptides are negatively charg ed with clusters of hydrophobic residues rich in phenylalanine, whereas the CaM-binding peptides are positively charged and often contain an Arg/Lys-T rp motif. The binding preferences identified with peptide libraries are con sistent with the features of the CnB-binding domains of all CnA isoforms an d the CaM-binding domains of CaM targets. (C) 1999 Elsevier Science B.V. Al l rights reserved.