Conformational regulation and target-myristoyl switch of calcineurin B homologous protein 3

Calcineurin B homologous protein 3 (CHP3) is an EF-hand Ca(2+)-binding protein involved in regulation of cancerogenesis, cardiac hypertrophy, and neuronal development through interactions with sodium/proton exchangers (NHEs) and signalling proteins. While the importance of Ca(2+) binding and myristoylation for CHP3 function has been recognized, the underlying molecular mechanism remained elusive. In this study, we demonstrate that Ca(2+) binding and myristoylation independently affect the conformation and functions of human CHP3. Ca(2+) binding increased local flexibility and hydrophobicity of CHP3 indicative of an open conformation. The Ca(2+)-bound CHP3 exhibited a higher affinity for NHE1 and associated stronger with lipid membranes compared to the Mg(2+)-bound CHP3, which adopted a closed conformation. Myristoylation enhanced the local flexibility of CHP3 and decreased its affinity to NHE1 independently of the bound ion, but did not affect its binding to lipid membranes. The data exclude the proposed Ca(2+)-myristoyl switch for CHP3. Instead, a Ca(2+)-independent exposure of the myristoyl moiety is induced by binding of the target peptide to CHP3 enhancing its association to lipid membranes. We name this novel regulatory mechanism ‘target-myristoyl switch’. Collectively, the interplay of Ca(2+) binding, myristoylation, and target binding allows for a context-specific regulation of CHP3 functions.