Interactions between model target peptide melittin (ME) and Euplotes octocarinatus centrin (EoCen) were investigated by fluorescence spectra, circular dichroism (CD) spectra and native polyacrylamide gel electrophoresis (PAGE). In 0.1 mol/L N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (Hepes) and 150 mmol/L NaCl at pH 7.4, EoCen and isolated short C-terminal domain of EoCen (SC-EoCen) form 1:1 peptide:protein complexes. However, no detectable signal changes can be observed while isolated N-terminal domain of EoCen (N-EoCen) or isolated long C-terminal domain of EoCen (LC-EoCen) was added into solution of ME. The interaction between EoCen and ME is specified exclusively for the short C-terminal domain of EoCen. On the basis of fluorescence titration curves, the conditional binding constants of ME with EoCen and SC-EoCen were calculated to be logKME-EoCen = 6.81±0.33 and log- KME-SC-EoCen = 6.51±0.45, respectively.
