Copper(I)-Alkyl Sulfide And -Cysteine Tri-Nuclear Clusters As Models For Metallo Proteins: A Structural Density Functional Analysis

After having set up the computational methodology for Cu(I)-sulfur systems as models for copper proteins, namely using the simple ligands H2S, HS-, CH3SH, and CH3S-, the Cu(I)-Cysteine systems have been investigated: [Cu-I(S-H(2)Cys)(n)](+) (H(2)Cys, cysteine, NH2,SH,COOH) [Cu-I(S-HCys)(n)](1-n) (NH2,S-,COOH). Finally, the structures for bi-nuclear [Cu-I((S) under bar - S(H)Et)(2)](2)(2+) (Et, CH2CH3), [Cu-I((S) under bar - SEt)(2)](2)(2-) and tri-nuclear [Cu-I(S-SH)](3), [Cu-I((S) under bar - SH)(2)](3)(3-) , [Cu-I((S) under bar - S(H)Et)(2)](3)(3+), [Cu-I((S) under bar - SEt)(2)](3)(3-) , [Cu-I((S) under bar - H(2)Cys)(2)](3)(3+) (NH2,SH,COOH), [Cu-I((S) under bar - HCys)(2)](3)(3-) (NH2,S-, COOH, and NH2,SH,COO-), as well as [Cu-I((S) under bar - Cys)(2)](3)(9-) (NH2,S-,COO-), were also optimized to mimic the active center for a metallo-chaperone copper transport protein (CopZ). The X-ray structures for the biomolecules were matched fairly well as regards the Cu-S bond distances and Cu center dot center dot center dot Cu contact distances in the case the model cysteine S atom is deprotonated. Upon protonation of ligand S atoms, the conformation of clusters is altered and might bring about the di- and tri-nuclear core breakage. These findings suggest that subtle protonation/deprotonation steps, i.e. small and/or local pH changes play a significant role for copper transport processes.