An ab Initio Quantum-Chemical Study of the Blue-Copper Site of Azurin

• Published in: Journal of the American Chemical Society 2002-03, Vol.124 (9), p.2035-2041
• Main Authors: van Gastel, M, Coremans, J. W. A, Sommerdijk, H, van Hemert, M. C, Groenen, E. J. J
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Azurin - chemistry; Binding Sites; Biological and medical sciences; Copper - chemistry; Fundamental and applied biological sciences. Psychology; Histidine - chemistry; Metalloproteins; Models, Molecular; Other metalloproteins; Proteins; Pseudomonas aeruginosa - chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0028166

The electronic structure of the blue-copper site of Pseudomonas aeruginosa azurin has been investigated by ab initio multireference determinantal configuration interaction (MRD-CI) calculations. A truncated site consisting of copper and its three equatorial ligands has been studied with emphasis on the g tensor and the nitrogen hyperfine tensors of the coordinating histidines. In the ground state the singly occupied molecular orbital (SOMO) involves a copper 3d orbital π antibonded to the cysteine sulfur and σ antibonded to the histidine nitrogens. A proper description of the electron-paramagnetic-resonance parameters has been achieved through the use of an effective core potential for copper up to and including the 3s electrons. Both the complete g tensor and the anisotropic hyperfine tensors at the nitrogens are essentially reproduced. Mulliken spin densities of 35 and 59% on copper and sulfur, respectively, and 2.1 and 1.7% on the respective coordinating nitrogens reflect the delocalized character of the SOMO and the inequivalence of the histidines.