A glutamate bridge is essential for dimer stability and metal selectivity in manganese superoxide dismutase.
In Escherichia coli manganese superoxide dismutase (MnSOD), the absolutely conserved Glu170 of one monomer is hydrogen-bonded to the Mn ligand His171 of the other monomer, forming a double bridge at the dimer interface. Point mutation of Glu170 --> Ala destabilizes the dimer structure, and the mutant protein occurs as a mixture of dimer and monomer species. The purified E170A MnSOD contains exclusively Fe and is devoid of superoxide dismutase activity. E170A Fe2-MnSOD closely resembles authentic FeSOD in terms of spectroscopic properties, anion interactions and pH titration behavior. Reconstitution of E170A Fe2-MnSOD with Mn(II) salts does not restore superoxide dismutase activity despite the spectroscopic similarity between E170A Mn2-MnSOD and wild type Mn2-MnSOD. Growth of sodA+ and sodA- E. coli containing the mutant plasmid pDT1-5(E170A) is impaired, suggesting that expression of mutant protein is toxic to the host cells.
Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science and Technology, Portland, Oregon 97291-1000, USA.
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Whittaker
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Whittaker
D001665:Binding Sites; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development; D018698:Glutamic Acid / Q000737:chemistry / Q000378:metabolism*; D006860:Hydrogen Bonding; D008345:Manganese / Q000737:chemistry*; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D013057:Spectrum Analysis; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D018698:Glutamic Acid; D008345:Manganese; D013482:Superoxide Dismutase