Scott D L, White S P, Otwinowski Z, Yuan W, Gelb M H, Sigler P B
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511.
Science. 1990 Dec 14;250(4987):1541-6. doi: 10.1126/science.2274785.
A chemical description of the action of phospholipase A2 (PLA2) can now be inferred with confidence from three high-resolution x-ray crystal structures. The first is the structure of the PLA2 from the venom of the Chinese cobra (Naja naja atra) in a complex with a phosphonate transition-state analogue. This enzyme is typical of a large, well-studied homologous family of PLA2S. The second is a similar complex with the evolutionarily distant bee-venom PLA2. The third structure is the uninhibited PLA2 from Chinese cobra venom. Despite the different molecular architectures of the cobra and bee-venom PLA2s, the transition-state analogue interacts in a nearly identical way with the catalytic machinery of both enzymes. The disposition of the fatty-acid side chains suggests a common access route of the substrate from its position in the lipid aggregate to its productive interaction with the active site. Comparison of the cobra-venom complex with the uninhibited enzyme indicates that optimal binding and catalysis at the lipid-water interface is due to facilitated substrate diffusion from the interfacial binding surface to the catalytic site rather than an allosteric change in the enzyme's structure. However, a second bound calcium ion changes its position upon the binding of the transition-state analogue, suggesting a mechanism for augmenting the critical electrophile.
现在可以从三个高分辨率X射线晶体结构中可靠地推断出磷脂酶A2（PLA2）作用的化学描述。第一个是中华眼镜蛇（Naja naja atra）毒液中的PLA2与膦酸酯过渡态类似物形成复合物的结构。这种酶是一个经过充分研究的大型同源PLA2家族的典型代表。第二个是与进化距离较远的蜂毒PLA2形成的类似复合物。第三个结构是中华眼镜蛇毒液中未受抑制的PLA2。尽管眼镜蛇毒和蜂毒PLA2的分子结构不同，但过渡态类似物与两种酶的催化机制的相互作用方式几乎相同。脂肪酸侧链的排列表明底物从其在脂质聚集体中的位置到与活性位点进行有效相互作用存在一条共同的进入途径。将眼镜蛇毒复合物与未受抑制的酶进行比较表明，在脂质-水界面处的最佳结合和催化是由于底物从界面结合表面到催化位点的扩散更容易，而不是酶结构的变构变化。然而，第二个结合的钙离子在过渡态类似物结合时会改变其位置，这表明存在一种增强关键亲电试剂的机制。
