Unique structural features of the monomeric Cu,Zn superoxide dismutase from Escherichia coli, revealed by X-ray crystallography

• Published in: Journal of molecular biology 1997-12, Vol.274 (3), p.408-420
• Main Authors: Pesce, Alessandra, Capasso, Clemente, Battistoni, Andrea, Folcarelli, Silvia, Rotilio, Giuseppe, Desideri, Alessandro, Bolognesi, Martino
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Binding Sites; copper enzymes; Crystallography, X-Ray; Cu,Zn superoxide dismutase; enzyme evolution; Escherichia coli - enzymology; Models, Molecular; Molecular Sequence Data; monomeric superoxide dismutase; Protein Conformation; Sequence Homology, Amino Acid; Superoxide Dismutase - chemistry; Superoxide Dismutase - metabolism; X-ray crystal structure
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1006/jmbi.1997.1400

The first three-dimensional structure of a functional monomeric Cu,Zn superoxide dismutase (from Escherichia coli, E_SOD) is reported at 2.0 Å resolution ( R-factor=16.8%). Compared to the homologous eukaryotic enzymes, E_SOD displays a perturbed antiparallel β-barrel structure. The most striking structural features observed include extended amino acid insertions in the surface 1,2-loop and S-S subloop, modification of the disulfide bridge connection, and loss of functional electrostatic residues, suggesting a modified control of substrate steering toward the catalytic center. The active site Cu 2+displays a distorted coordination sphere due to an unusually long bond to the metal-bridging residue His61. Inspection of the crystal packing does not show regions of extended contact indicative of a dimeric assembly. The molecular surface region involved in subunit dimerization in eukaryotic superoxide dismutases is structurally altered in E_SOD and displays a net polar nature.