Analysis of the role of Mg 2+ on conformational change and target recognition by Ciliate Euplotes octocarinatus centrin

Abstract

The binding of Mg 2+ with the Euplotes octocarinatus centrin (EoCen) and the effect of Mg 2+ on the binding of EoCen with the peptide melittin were examined by spectroscopic methods. In this study, it was found that Mg 2+ may bind with Ca 2+-binding sites, at least partly, on EoCen, which displays ∼10-fold weaker affinity than Ca 2+. In the presence of Mg 2+, Ca 2+-saturated EoCen undergoes significant conformational changes resulting in decreased exposure of hydrophobic surfaces on the protein. Additionally, excess Mg 2+ did not change the stoichiometry, but rather reduced the affinity of EoCen to melittin. The Mg 2+-dependent decrease in the affinities of EoCen to melittin is an intrinsic property of Mg 2+, rather than a nonspecific ionic effect. The inhibitory effect of Mg 2+ on the formation of complexes between EoCen and melittin may contribute to the specificity of EoCen in target activation in response to cellular Ca 2+ concentration fluctuations.