The functional and structural significance of the intrasubunit disulfide bond in copper-zinc superoxide dismutase (SOD1) was studied by characterizing mutant forms of human SOD1 (hSOD) and yeast SOD1 lacking the disulfide bond. We determined x-ray cr ...
The functional and structural significance of the intrasubunit disulfide bond in copper-zinc superoxide dismutase (SOD1) was studied by characterizing mutant forms of human SOD1 (hSOD) and yeast SOD1 lacking the disulfide bond. We determined x-ray crystal structures of metal-bound and metal-deficient hC57S SOD1. C57S hSOD1 isolated from yeast contained four zinc ions per protein dimer and was structurally very similar to wild type. The addition of copper to this four-zinc protein gave properly reconstituted 2Cu,2Zn C57S hSOD, and its spectroscopic properties indicated that the coordination geometry of the copper was remarkably similar to that of holo wild type hSOD1. In contrast, the addition of copper and zinc ions to apo C57S human SOD1 failed to give proper reconstitution. Using pulse radiolysis, we determined SOD activities of yeast and human SOD1s lacking disulfide bonds and found that they were enzymatically active at ∼10% of the wild type rate. These results are contrary to earlier reports that the intrasubunit disulfide bonds in SOD1 are essential for SOD activity. Kinetic studies revealed further that the yeast mutant SOD1 had less ionic attraction for superoxide, possibly explaining the lower rates. Saccharomyces cerevisiae cells lacking the sod1 gene do not grow aerobically in the absence of lysine, but expression of C57S SOD1 increased growth to 30-50% of the growth of cells expressing wild type SOD1, supporting that C57S SOD1 retained a significant amount of activity.
Organizational Affiliation:
From the Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, LG Chem, Ltd., Yuseong-gu, Daejeon 305-380, Korea.,From the Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, the Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798.,From the Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, the Department of Bioinspired Science, Ewha Womans University, Seoul 120-750, Korea jsv@chem.ucla.edu.,the Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, the Department of Veterans Affairs, South Texas Veterans Health Care System, San Antonio, Texas 78229, and.,From the Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, the Department of Chemical and Environmental Engineering, University of Arizona, Tucson, Arizona 85721.,From the Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, the Department of Wine Studies, Santa Rosa Junior College, Santa Rosa, California 95401, kevinsea@yahoo.com.,the Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229.,the Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973.,From the Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095.
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