Germin is a manganese containing homohexamer with oxalate oxidase and superoxide dismutase activities

Germin is a hydrogen peroxide generating oxalate oxidase with extreme therm al stability; it is involved in the defense against biotic and abiotic stre ss in plants. The structure, determined at 1.6 Angstrom resolution, compris es beta -jellyroll monomers locked into a homohexamer (a trimer of dimers), with extensive surface burial accounting for its remarkable stability. The germin dimer is structurally equivalent to the monomer of the 7S seed stor age proteins (vicilins), indicating evolution from a common ancestral prote in. A single manganese ion is bound per germin monomer by ligands similar t o those of manganese superoxide dismutase (MnSOD). Germin is also shown to have SOD activity and we propose that the defense against extracellular sup eroxide radicals is an important additional role for germin and related pro teins.