title: Metal-ligand interplay in blue copper proteins studied by 1H NMR spectroscopy: Cu(II)-pseudoazurin and Cu(II)-rusticyanin.
abstract: The blue copper proteins (BCPs), pseudoazurin from Achromobacter cycloclastes and rusticyanin from Thiobacillus ferrooxidans, have been investigated by (1)H NMR at a magnetic field of 18.8 T. Hyperfine shifts of the protons belonging to the coordinated ligands have been identified by exchange spectroscopy, including the indirect detection for those resonances that cannot be directly observed (the beta-CH(2) of the Cys ligand, and the NH amide hydrogen bonded to the S(gamma)(Cys) atom). These data reveal that the Cu(II)-Cys interaction in pseudoazurin and rusticyanin is weakened compared to that in classic blue sites (plastocyanin and azurin). This weakening is not induced by a stronger interaction with the axial ligand, as found in stellacyanin, but might be determined by the protein folding around the metal site. The average chemical shift of the beta-CH(2) Cys ligand in all BCPs can be correlated to geometric factors of the metal site (the Cu-S(gamma)(Cys) distance and the angle between the CuN(His)N(His) plane and the Cu-S(gamma)(Cys) vector). It is concluded that the degree of tetragonal distortion is not necessarily related to the strength of the Cu(II)-S(gamma)(Cys) bond. The copper-His interaction is similar in all BCPs, even for the solvent-exposed His ligand. It is proposed that the copper xy magnetic axes in blue sites are determined by subtle geometrical differences, particularly the orientation of the His ligands. Finally, the observed chemical shifts for beta-CH(2) Cys and Ser NH protons in rusticyanin suggest that a less negative charge at the sulfur atom could contribute to the high redox potential (680 mV) of this protein.
authors.affiliation: Biophysics Section and Instituto de Biología Molecular y Celular de Rosario (IBR), University of Rosario, Suipacha 531, S2002LRK Rosario, Argentina.
authors.forename: Antonio
authors.initials: A
authors.lastname: Donaire
authors.forename: Beatriz
authors.initials: B
authors.lastname: Jiménez
authors.forename: Claudio O
authors.initials: CO
authors.lastname: Fernández
authors.forename: Roberta
authors.initials: R
authors.lastname: Pierattelli
authors.forename: Tomotake
authors.initials: T
authors.lastname: Niizeki
authors.forename: José-María
authors.initials: JM
authors.lastname: Moratal
authors.forename: John F
authors.initials: JF
authors.lastname: Hall
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Kohzuma
authors.forename: S Samar
authors.initials: SS
authors.lastname: Hasnain
authors.forename: Alejandro J
authors.initials: AJ
authors.lastname: Vila
mesh_terms: D000421:Alcaligenes / Q000737:chemistry; D000595:Amino Acid Sequence; D001400:Azurin / Q000031:analogs & derivatives* / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011522:Protons; D013855:Thiobacillus / Q000737:chemistry
chemical_list: D008024:Ligands; D011522:Protons; C047163:pseudoazurin; C012543:rusticyanin; D001400:Azurin; D003300:Copper