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

锰超氧化物歧化酶（SODs）、铁超氧化物歧化酶（Fe-SODs）和形相型SODs，其主要包括牙龈型超氧化物歧化酶(P.g。SOD，具有很大程度的序列同源性和x射线结构相似性。P.g.-SOD的Gly155位于活性金属位点11Å左右，在mn - sod的排列氨基酸序列中大多保守，但在大多数fe - sod中被Thr取代。为了弄清金属比活度的结构基础，我们利用高场电子顺磁共振谱分析了金属比活度。我们发现Gly155Thr突变使金属特异性活性从形生型急剧改变为接近铁特异性活性。此外，p.g.s osod的Gly155Thr突变体改变了Mn（II）光谱，使其与大肠杆菌中Mn取代Fe SOD的光谱非常相似。结果表明，Gly155作为决定锰比活性的氨基酸残基具有通用性，同一位置上的Thr作为决定sod上铁比活性的氨基酸残基具有通用性。

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.