Nickel superoxide dismutase structure and mechanism

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Superoxide dismutases (SODs) are critical enzymes protecting against oxidative stress.
• Nickel-containing SODs (NiSODs) represent a distinct class with unique catalytic mechanisms.
• Understanding NiSOD structure is key to elucidating its function and evolutionary relationships.

Purpose of the Study:

• To determine the high-resolution crystal structure of nickel superoxide dismutase (NiSOD).
• To characterize the novel Ni active site, protein fold, and assembly of NiSOD.
• To elucidate the molecular mechanisms of NiSOD catalysis and maturation.

Main Methods:

• X-ray crystallography at 1.30 Å resolution.
• Analysis of apo and holo NiSOD structures.
• Comparison with other metallo-SOD structures (Cu,Zn and Mn/Fe SODs).

Main Results:

• A novel hexameric NiSOD fold featuring 4-helix bundles and N-terminal Ni-chelating hooks was identified.
• A conserved nine-residue Ni-hook motif (His-Cys-X-X-Pro-Cys-Gly-X-Tyr) is critical for Ni binding and catalysis.
• Ni active site geometry cycles between square planar Ni(II) and square pyramidal Ni(III) states, consistent with EPR spectroscopy.
• Conserved lysine residues facilitate substrate access to the active site.

Conclusions:

• The NiSOD crystal structure reveals a unique fold, assembly, and Ni active site, distinct from other SODs.
• The Ni-hook motif is a defining feature of NiSODs, essential for metal binding and catalytic activity.
• Structure-function relationships in NiSOD provide insights into enzyme maturation, catalysis, and conserved SOD mechanisms.