The effect of Trp83 mutant on the properties of CopC

Spectral studies on the interaction between HSSC and apoCopC

The interaction between HSSC (SSC = salicylaldehyde semicarbazone anion) and apoCopC has been investigated in detail by means of UV, fluorescence and fluorescence lifetime measurement in 10 mM Hepes buffer, at pH 7.4, 25°C. The results suggested that HSSC can form a novel supramolecular system with apoCopC, which can form a 1:1 host-guest inclusion supramolecular complex with HSSC, and the forming constant had been calculated to be (8.83±0.32)×10(5) M(-1). It suggested the strong inclusion ability of apoCopC to the guest molecules. In addition, the stoichiometric ratio of Cu(2+) and HSSC was 1:1, which was the same as Cu(2+) and apoCopC. However, the binding ability between Cu(2+) and HSSC was much weaker than that between Cu(2+) and apoCopC. Moreover, the binding ability of HSSC with Cu(2+) has an effect on the binding ability between HSSC and apoCopC, and vice versa. The reason attributed to this effect was that the formation of hydrogen bond between Met46 in apoCopC and the phenolic hydroxyl of HSSC participated in the copper coordination. Furthermore, it was also found that HSSC quench the fluorescence of apoCopC by the static quenching process and the number of binding site was calculated. The thermodynamic parameters ΔH°, ΔS° and ΔG° at different temperatures were obtained. The formation of apoCopC-HSSC complex depended on the cooperation of the van der Waals force and hydrogen bond, and the binding average distance between apoCopC and HSSC was determined. What is more, the binding site of HSSC to apoCopC was shown vividly by an automated public domain software package ArgusLab 4.0.1.