线虫MnSOD-3参与了长寿途径,其催化机制与衰老过程和致癌作用有关。MnSOD-3的结构提供了四聚体界面(残基41-54)动态区域的独特晶体学证据。我们已将MnSOD-3-叠氮化物络合物的结构确定为1.77-µ分辨率。对这种复合物的分析表明,底物模拟,叠氮化物,末端结合到锰中心作为第六个配体,并且它直接连接到第三个和新的溶剂分子,该溶剂分子也位于与底物进入漏斗的His30和Tyr34残基相互作用的距离内。这是真核MnSOD-叠氮化物复合物的第一个结构,不间断的氢键网络,形成包含三个外球溶剂分子的质子继电器,模拟基板,网关残留物,Gln142和溶剂配体。这种构型支持过氧化氢产物的形成和释放,这与MnSOD的5-6-5催化机理一致。MnSOD-3的高产物解离常数k4反映了低产物抑制,使得该酶即使在高水平的超氧化物下也是有效的。
C. elegans MnSOD-3 has been implicated in the longevity pathway and its mechanism of catalysis is relevant to the aging process and carcinogenesis. The structures of MnSOD-3 provide unique crystallographic evidence of a dynamic region of the tetrameric interface (residues 41-54). We have determined the structure of the MnSOD-3-azide complex to 1.77-Å resolution. Analysis of this complex shows that the substrate analog, azide, binds end-on to the manganese center as a sixth ligand and that it ligates directly to a third and new solvent molecule also positioned within interacting distance to the His30 and Tyr34 residues of the substrate access funnel. This is the first structure of a eukaryotic MnSOD-azide complex that demonstrates the extended, uninterrupted hydrogen-bonded network that forms a proton relay incorporating three outer sphere solvent molecules, the substrate analog, the gateway residues, Gln142, and the solvent ligand. This configuration supports the formation and release of the hydrogen peroxide product in agreement with the 5-6-5 catalytic mechanism for MnSOD. The high product dissociation constant k4 of MnSOD-3 reflects low product inhibition making this enzyme efficient even at high levels of superoxide.