Contribution of the amino acid residues located near the active site metal to the metal-specific activity of Porphyromonas gingivalis SOD induced by a double mutation of Leu 72 Trp and Leu 76 Phe

[Summary] The role of superoxide dismutase (SOD) as a radical scavenger in Porphyromonas gingivalis is well documented. P.gingivalis SOD (Pg SOD), which is characterized by a metal-tolerant activity, can use either iron or manganese as a cofactor. Leu 72 and Leu 76, located near the active-site metal, are characteristic amino acid sequences of Pg SOD proteins, although they are substituted to Trp in the 72 position and Phe in the 76 position in most iron-containing SOD (Fe-SOD) proteins. In the present study, we constructed a mutant of the enzyme with changes from Leu 72 to Trp and Leu 76 to Phe. This mutant SOD was examined with respect to its metal-dependent activity and structural characterization. We herein conclude the integrity of Leu 72 and Leu 76 is a necessary requisite for the metal-tolerant activity of Pg SOD.