Backbone and side-chain resonance assignments of (Ca)-calmodulin bound to beta calcineurin A CaMBD peptide.

Calcineurin (CaN) is a heterodimeric and highly conserved serine/threonine phosphatase (PP2B) that plays a critical role in coupling calcium signals to physiological processes including embryonic cardiac development, NF-AT-regulated gene expression in immune responses, and apoptosis. The catalytic subunit (CaN) has three isoforms (α, β, and γ,) in humans and seven isoforms in Paramecium. In all eukaryotes, the EF-hand protein calmodulin (CaM) regulates CaN activity in a calcium-dependent manner. The N- and C-domains of CaM (CaM and CaM) recognize a CaM-binding domain (CaMBD) within an intrinsically disordered region of CaN that precedes the auto-inhibitory domain (AID) of CaN. Here we present nearly complete H, C, and N resonance assignments of (Ca)-CaM bound to a peptide containing the CaMBD sequence in the beta isoform of CaN (βCaN-CaMBDp). Its secondary structure elements predicted from the assigned chemical shifts were in good agreement with those observed in the high-resolution structures of (Ca)-CaM bound to CaMBDs of multiple enzymes. Based on the reported literature, the CaMBD of the α isoform of CaN can bind to CaM in two opposing orientations which may influence the regulatory function of CaM. Because a high resolution structure of (Ca)-CaM bound to βCaN-CaMBDp has not been reported, our studies serve as a starting point for determining the solution structure of this complex. This will demonstrate the preferred orientation of (Ca)-CaM on the CaMBD as well as the orientations of CaM and CaM relative to each other and to the AID of βCaN.