Mechanism of Orlistat Hydrolysis by the Thioesterase of Human Fatty Acid Synthase.
Mechanism of Orlistat Hydrolysis by the Thioesterase of Human Fatty Acid Synthase.
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DOI：
10.1021/cs500956m
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发表时间：
2014-10-03
期刊：
影响因子：
12.9
通讯作者：
Liu, Jing-Yuan
中科院分区：
文献类型：
--
作者：
Fako, Valerie E.;Zhang, Jian-Ting;Liu, Jing-Yuan
脂肪酸合酶（FASN）是唯一能够从头合成游离脂肪酸的蛋白质，在多种人类癌症中过度表达，并且与这些癌症的不良预后和侵袭性相关。奥利司他是 FDA 批准的用于治疗肥胖症的药物，可抑制胃肠道中的胰腺脂肪酶，也可抑制人类 FASN 的硫酯酶 (TE)。 TE与奥利司他的共晶结构显示了假TE二聚体，其活性位点含有两种不同形式的奥利司他，是与丝氨酸残基（Ser2308）共价结合的中间体以及水解和灭活的产物。在本研究中，我们试图通过分子动力学模拟研究共价结合的奥利司他的己基尾部在水活化水解中的作用来了解 TE 催化奥利司他水解的机制。我们发现共价结合的奥利司他的己基尾部经历了构象转变，这伴随着奥利司他的羟基部分和TE的催化His2481之间的氢键的不稳定，进而导致水分子和His2481之间的氢键增加以及水活化水解奥利司他和Ser2308之间的共价键的机会增加。因此，奥利司他的己基尾部的构象在奥利司他水解中起着重要作用。稳定己基尾部的策略可能会导致设计出更有效的不可逆抑制剂，这些抑制剂以 FASN 为目标，并以更大的持久性阻断 TE 活性。
Fatty acid synthase (FASN), the sole protein capable of de novo synthesis of free fatty acids, is overexpressed in a wide variety of human cancers and is associated with poor prognosis and aggressiveness of these cancers. Orlistat, an FDA-approved drug for obesity treatment that inhibits pancreatic lipases in the GI tract, also inhibits the thioesterase (TE) of human FASN. The cocrystal structure of TE with orlistat shows a pseudo TE dimer containing two different forms of orlistat in the active site, an intermediate that is covalently bound to a serine residue (Ser2308) and a hydrolyzed and inactivated product. In this study, we attempted to understand the mechanism of TE-catalyzed orlistat hydrolysis by examining the role of the hexyl tail of the covalently bound orlistat in water activation for hydrolysis using molecular dynamics simulations. We found that the hexyl tail of the covalently bound orlistat undergoes a conformational transition, which is accompanied by destabilization of a hydrogen bond between a hydroxyl moiety of orlistat and the catalytic His2481 of TE that in turn leads to an increased hydrogen bonding between water molecules and His2481 and increased chance for water activation to hydrolyze the covalent bond between orlistat and Ser2308. Thus, the conformation of the hexyl tail of orlistat plays an important role in orlistat hydrolysis. Strategies that stabilize the hexyl tail may lead to the design of more potent irreversible inhibitors that target FASN and block TE activity with greater endurance.
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