NMR IDENTIFICATION OF CALCINEURIN-B RESIDUES AFFECTED BY BINDING OF A CALCINEURIN-A PEPTIDE

Triple resonance 3D NMR methods have been used to study the interaction between calcineurin B and a peptide fragment of calcineurin A for which it has high affinity (K-D similar to 4 x 10(-7) M), Although calcineurin B aggregates at NMR concentrations of similar to 1 mM, in the presence of a target peptide fragment of calcineurin A it becomes monomeric and yields NMR spectra that are very similar to those reported previously for calcineurin B solubilized by the zwitterionic detergent CHAPS, Changes in chemical shifts between CHAPS- and peptide-solubilized calcineurin B are small which is indicative of no differences in secondary structure, Residues most affected by binding to target peptide are found primarily on the hydrophobic faces of the four helices, present in each of the two globular domains in calcineurin B, and in the loops connecting helices II and III, IV and V, and possibly in the C-terminal 12 residues, which also exhibit a change in mobility.