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  • Title: Conversion of the metal-specific activity of Escherichia coli Mn-SOD by site-directed mutagenesis of Gly165Thr.
    Author: Osawa M, Yamakura F, Mihara M, Okubo Y, Yamada K, Hiraoka BY.
    Journal: Biochim Biophys Acta; 2010 Sep; 1804(9):1775-9. PubMed ID: 20451673.
    Abstract:
    Glycine 165, which is located near the active site metal, is mostly conserved in aligned amino acid sequences of manganese-containing superoxide dismutase (Mn-SOD) proteins, but is substituted to threonine in most iron-containing SODs (Fe-SODs). Because threonine 165 is located between Trp128 and Trp130, and Trp128 is one of the metal-surrounding aromatic amino acids, the conversion of this amino acid may affect the metal-specific activity of Escherichia coli Mn-SOD. In order to clarify this possibility, we prepared a mutant of E. coli Mn-SOD with the replacement of Gly165 by Thr. The ratio of the specific activities of Mn- to Fe-reconstituted enzyme increased from 0.006 in the wild-type to 0.044 in the mutant SOD; therefore, the metal-specific SOD was converted to a metal-tolerant SOD. The visible absorption spectra of the Fe- and Mn-reconstituted mutant SODs indicated the loss of Mn-SOD character. It was concluded that Gly at position 165 plays a catalytic role in maintaining the integrity of the metal specificity of Mn-SOD.
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