Department of Biochemistry, Indian Institute of Science, Bengaluru, 560012, India; Molecular Biophysics Unit, Indian Institute of Science, Bengaluru, 560012, India; Centre for DNA Fingerprinting and Diagnostics, Hyderabad, 500007, India. Electronic address: [Email]
Superoxide dismutase, known to gain large rate enhancement on dimerization, forms a homodimer stabilized by hydrogen bonding between a number of internal water molecules and a few amino acid residues at the interface. Within each subunit the β-sheets provide a sequence of delocalized π-electron units of peptide bonds alternating with hydrogen bonds referred as π-H pathway. These pathways in the two subunits in the dimer are interlinked through a chain of four water molecules bridged by hydrogen bonds at the interface. Connecting the two Cu-centers this π-H pathway can enable rapid electron transfer from one superoxide molecule to the other, crucial for the catalytic reaction and the high rate in the dimer. A proton relay of hydrogen-bonded water molecules in the dimer translocates protons to form the product, hydrogen peroxide.