Cation-pi Interactions and oxidative effects on Cu+ and Cu2+ binding to Phe, Tyr, Trp, and His amino acids in the gas phase. Insights from first-principles calculations.
The coordination properties of the four natural aromatic amino acids (AA(arom) = Phe, Tyr, Trp, and His) to Cu+ and Cu2+ have been exhaustively studied by means of ab initio calculations. For Cu+-Phe, Cu+-Tyr and Cu+-Trp, the two charge solvated tridentate N/O/ring and bidentate N/ring structures, with the metal cation interacting with the pi system of the ring, were found to be the lowest ones, relative DeltaG(298K) energies being less than 0.5 kcal/mol. The Cu+-His ground-state structure has the metal cation interacting with the NH2 group and the imidazole N. For these low-lying structures vibrational features are also discussed. Unlike Cu+ complexes, the ground-state structure of Cu2+-Phe, Cu2+-Tyr, and Cu2+-Trp does not present cation-pi interactions due to the oxidation of the aromatic ring induced by the metal cation. The ground-state structure of Cu2+-His does not present oxidation of the amino acid, the coordination to Cu2+ being tridentate with the oxygen of the carbonyl group, the nitrogen of the amine, and the N of the imidazole. Other less stable isomers, however, show oxidation of His, particularly of the imidazole ring, which can induce spontaneous proton-transfer reactions from the NH of the imidazole to the NH2 of the backbone. Finally, the computed binding energies for Cu+-AA(arom) and Cu2+-AA(arom) systems have been computed, the order found for the single charged systems being Cu+-His > Cu+-Trp > Cu+-Tyr > Cu+-Phe, in very good agreement with the experimental data.
Rimola
Albert
A
Departament de Química, Universitat Autonoma de Barcelona, Bellaterra 08193, Spain.
Rodríguez-Santiago
Luis
L
Sodupe
Mariona
M
D000465:Algorithms; D024322:Amino Acids, Aromatic / Q000737:chemistry*; D001665:Binding Sites; D002413:Cations, Divalent; D003300:Copper / Q000737:chemistry*; D005740:Gases; D006639:Histidine / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010649:Phenylalanine / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry
D024322:Amino Acids, Aromatic; D002413:Cations, Divalent; D005740:Gases; D012997:Solvents; D014443:Tyrosine; D010649:Phenylalanine; D006639:Histidine; D003300:Copper; D014364:Tryptophan; D009584:Nitrogen; D010100:Oxygen