A change of the metal-specific active site structure of superoxide dismutase from Porphyromonas gingivalis by the mutation of Gly155Thr.

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Mn-superoxide dismutases (SODs), Fe-SODs and cambialistic SODs, its include P.gingivalis (P.g.) SOD, have a large degree of sequence homology and X-ray structural similarity. Gly155 of P.g.-SOD is located about 11Å from active metal sites and is mostly conserved in aligned amino acid sequences of Mn-SODs, but is substituted for Thr in most Fe-SODs. In order to clarify the structural bases of the metal-specific activity, we analyzed using high-field electron paramagnetic resonance spectroscopy.We found that Gly155Thr mutation changes the metal-specific activity drastically from a cambialistic type to close to Fe-specific type. Also the Gly155Thr mutant of P.g.-SOD changed the Mn(II) spectrum so that it closely resembled the spectrum of Mn-substituted Fe SOD from E.coli. It has been concluded that Gly155 had universality as one of the amino acid residue which determines the Mn specific activity and Thr on same position had universality as one of the amino acid residue which determines the Fe specifc activity on SODs.