Crystal structure of Enpp1, an extracellular glycoprotein involved in bone mineralization and insulin signaling
Crystal structure of Enpp1, an extracellular glycoprotein involved in bone mineralization and insulin signaling
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DOI：
10.1073/pnas.1208017109
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发表时间：
2012-10-16
影响因子：
11.1
通讯作者：
Nureki, Osamu
中科院分区：
文献类型：
--
作者：
Kato, Kazuki;Nishimasu, Hiroshi;Nureki, Osamu
Enpp1是一种膜结合糖蛋白，通过水解细胞外核苷酸三磷酸产生焦磷酸盐来调节骨矿化。Enpp1功能障碍导致以异位钙化为特征的人类疾病。Enpp1也抑制胰岛素信号传导，并且Enpp1多态性与胰岛素抵抗有关。然而，Enpp1在这些细胞过程中发挥作用的确切机制仍然难以捉摸。在这里，我们报道了小鼠Enpp1与四种不同的单磷酸核苷酸复合物的细胞外区域的晶体结构，分辨率为2.7-3.2埃。核苷酸被安置在催化结构域中由插入环形成的口袋中，这解释了Enpp1对ATP底物的偏好。疾病相关突变的结构作图表明域间相互作用的功能重要性。通过对溶血磷脂酶D的结构比较，发现Enpp1与Enpp2在结构域排列和活性位点结构上存在显著差异。值得注意的是，缺乏插入环的Enpp1突变体失去了核苷酸水解活性，而获得了Enpp2的溶血磷脂水解活性。我们的发现为Enpp家族蛋白如何进化以发挥其不同的细胞功能提供了结构上的见解。
Enpp1 is a membrane-bound glycoprotein that regulates bone mineralization by hydrolyzing extracellular nucleotide triphosphates to produce pyrophosphate. Enpp1 dysfunction causes human diseases characterized by ectopic calcification. Enpp1 also inhibits insulin signaling, and an Enpp1 polymorphism is associated with insulin resistance. However, the precise mechanism by which Enpp1 functions in these cellular processes remains elusive. Here, we report the crystal structures of the extracellular region of mouse Enpp1 in complex with four different nucleotide monophosphates, at resolutions of 2.7-3.2 angstrom. The nucleotides are accommodated in a pocket formed by an insertion loop in the catalytic domain, explaining the preference of Enpp1 for an ATP substrate. Structural mapping of disease-associated mutations indicated the functional importance of the interdomain interactions. A structural comparison of Enpp1 with Enpp2, a lysophospholipase D, revealed marked differences in the domain arrangements and active-site architectures. Notably, the Enpp1 mutant lacking the insertion loop lost the nucleotide-hydrolyzing activity but instead gained the lysophospholipid-hydrolyzing activity of Enpp2. Our findings provide structural insights into how the Enpp family proteins evolved to exert their diverse cellular functions.