Computer simulation of the interaction of Cu(I) with cys residues at the binding site of the yeast metallochaperone Cu(I)-Atx1.

The copper binding site and electronic structure of the metallochaperone protein Atx1 were investigated using the combination of quantum mechanics methods and molecular mechanics methods in the ONIOM(QM:MM) scheme at the density functional theory (DFT) B3LYP/ 6-31G(d):AMBER level. The residues in the binding site, -Met13-Thr14-Cys15-Cu(I)-Cys18-Gly17-Ser16-, were modeled with QM and the rest of the residues with MM. Our results indicate that the structure for Cu(I)-Atx1 has the copper atom coordinated to two sulfur atoms from Cys15 (2.110 A) and Cys18 (2.141 A) with an angle S-Cu(I) -S of 166 degrees . The potential energy surface of the copper atom is used to estimate its binding energy and the force field for the copper ligands. The potential surface is shallow for the bending mode S-Cu-S, which explains the origin of the disorder observed in crystallographic and nuclear magnetic resonance studies. Using molecular dynamics for Cu(I)-Atx1 in a box of water molecules and in vacuum, with the force field derived in this work, we observed a correlated motion between the side chains of Thr14 and of Lys65 which enhances distortions in the S-Cu-S geometry. The results are compared with recent experiments and the previous models. The vibrational spectra for the copper ligands and for the residues in the binding site were computed. The localized modes for the copper ligands and the amide bands were assigned. The presence of the copper atom affects the amide bands' frequencies of the residues Cys15 and Cys18, giving resolved bands that can be used to sense changes in the binding site upon translocation of copper atom or interaction with target proteins. Furthermore, the EXAFS (extended X-ray absorption fine structure) spectrum of the proposed structure for Cu(I)-Atx1 was calculated and reproduced the experiments fairly well.