Structural basis of the sphingomyelin phosphodiesterase activity in neutral sphingomyelinase from Bacillus cereus
Structural basis of the sphingomyelin phosphodiesterase activity in neutral sphingomyelinase from Bacillus cereus
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DOI：
10.1074/jbc.m601089200
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发表时间：
2006-06-09
影响因子：
4.8
通讯作者：
Sakurai, Jun
中科院分区：
文献类型：
--
作者：
Ago, Hideo;Oda, Masataka;Sakurai, Jun
来自蜡状芽孢杆菌 (Bc-SMase) 的鞘磷脂酶 (SMase) 以二价金属离子依赖性方式将鞘磷脂水解为磷酸胆碱和神经酰胺。 Bc-SMase 是哺乳动物中性 SMase (nSMase) 的同源物，模仿内源性哺乳动物 nSMase 引起分化、发育、衰老和细胞凋亡的作用。因此，Bc-SMase 可能是表征较差的哺乳动物 nSMase 的良好模型。 Bc-SMase 鞘磷脂酶活性的金属离子激活顺序为 Co2+ >= Mn2+ >= Mg2+ >> Ca2+ >= Sr2+。确定了与 Co2+、Mg2+ 或 Ca2+ 结合的 Bc-SMase 的第一个晶体结构。 Co2+- 和 Mg2+- 结合形式的裂隙中心的水桥双二价金属离子被认为是鞘磷脂酶活性所需的催化结构。相比之下，该位点的 Ca2+ 结合结构仅显示一个结合位点。另一个单一金属结合位点存在于裂口的一侧边缘。基于结合位点残基的高度保守性，结合有 Mg2+ 或 Co2+ 的 Bc-SMase 晶体结构可能提供适用于属于 DNase I 样折叠超家族的磷酸水解酶的共同结构框架。此外，结构特征和定点诱变表明具有芳香族氨基酸残基的特定β-发夹参与与膜结合鞘磷脂底物的结合。
Sphingomyelinase (SMase) from Bacillus cereus (Bc-SMase) hydrolyzes sphingomyelin to phosphocholine and ceramide in a divalent metal ion-dependent manner. Bc-SMase is a homologue of mammalian neutral SMase (nSMase) and mimics the actions of the endogenous mammalian nSMase in causing differentiation, development, aging, and apoptosis. Thus Bc-SMase may be a good model for the poorly characterized mammalian nSMase. The metal ion activation of sphingomyelinase activity of Bc-SMase was in the order Co2+ >= Mn2+ >= Mg2+ >> Ca2+ >= Sr2+. The first crystal structures of Bc-SMase bound to Co2+, Mg2+, or Ca2+ were determined. The water-bridged double divalent metal ions at the center of the cleft in both the Co2+- and Mg2+-bound forms were concluded to be the catalytic architecture required for sphingomyelinase activity. In contrast, the architecture of Ca2+ binding at the site showed only one binding site. A further single metal-binding site exists at one side edge of the cleft. Based on the highly conserved nature of the residues of the binding sites, the crystal structure of Bc-SMase with bound Mg2+ or Co2+ may provide a common structural framework applicable to phosphohydrolases belonging to the DNase I-like folding superfamily. In addition, the structural features and site-directed mutagenesis suggest that the specific beta-hairpin with the aromatic amino acid residues participates in binding to the membrane-bound sphingomyelin substrate.