Allosteric Inhibition of Human Porphobilinogen Synthase
Allosteric Inhibition of Human Porphobilinogen Synthase
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DOI：
10.1074/jbc.m109.026294
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发表时间：
2009-12-18
影响因子：
4.8
通讯作者：
Jaffe, Eileen K.
中科院分区：
文献类型：
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作者：
Lawrence, Sarah H.;Ramirez, Ursula D.;Jaffe, Eileen K.
胆红素原合成酶(PBGS)催化四吡咯(如血红素、叶绿素)生物合成的第一步。人的PBGS作为高活性八聚体、低活性六聚体和交替二聚体配置的平衡存在，这些配置决定了进一步组装的化学计量和结构。据推测，可以发现通过稳定六聚体来抑制人PBGS活性的小分子。如果这种分子存在于环境中，可能会加剧与PBGS活性降低相关的疾病状态，如铅中毒和ALAD卟啉症，后者与人类PBGS变体的四级结构平衡向六聚体移动有关(Jaffe，E.K.和Stith，L.(2007)AmJ.嗯。吉内。80、329-337)。利用与人PBGS晶体结构的六聚体特定表面腔类似的111,000个结构的电子预筛选(对接)，鉴定了人PBGS的六聚体稳定抑制剂。77个化合物在体外进行了评估；其中3个化合物在天然PAGE迁移率变化分析中提供了90%-100%的八聚体到六聚体的转化率。在化学纯度的基础上，进一步评价了两个化合物(ML-3A9和ML-3H2)对四级结构平衡和酶活性的影响。自然发生的ALAD卟啉相关的人PBGS变体被证明对ML-3A9和ML-3H2的抑制增加了敏感性。ML-3H2是一种阿米巴杀菌剂的结构类似物，具有类似卟啉的副作用。数据支持这样一种假设，即人类PBGS六聚体的稳定性可能解释了这些副作用。目前的工作确定了人PBGS的变构配体，从而确定了人PBGS是一种医学上相关的变构酶。
Porphobilinogen synthase (PBGS) catalyzes the first common step in tetrapyrrole (e.g. heme, chlorophyll) biosynthesis. Human PBGS exists as an equilibrium of high activity octamers, low activity hexamers, and alternate dimer configurations that dictate the stoichiometry and architecture of further assembly. It is posited that small molecules can be found that inhibit human PBGS activity by stabilizing the hexamer. Such molecules, if present in the environment, could potentiate disease states associated with reduced PBGS activity, such as lead poisoning and ALAD porphyria, the latter of which is associated with human PBGS variants whose quaternary structure equilibrium is shifted toward the hexamer (Jaffe, E. K., and Stith, L. (2007) Am. J. Hum. Genet. 80, 329-337). Hexamer-stabilizing inhibitors of human PBGS were identified using in silico pre-screening (docking) of similar to 111,000 structures to a hexamer-specific surface cavity of a human PBGS crystal structure. Seventy-seven compounds were evaluated in vitro; three provided 90-100% conversion of octamer to hexamer in a native PAGE mobility shift assay. Based on chemical purity, two (ML-3A9 and ML-3H2) were subjected to further evaluation of their effect on the quaternary structure equilibrium and enzymatic activity. Naturally occurring ALAD porphyria-associated human PBGS variants are shown to have an increased susceptibility to inhibition by both ML-3A9 and ML-3H2. ML-3H2 is a structural analog of amebicidal drugs, which have porphyria-like side effects. Data support the hypothesis that human PBGS hexamer stabilization may explain these side effects. The current work identifies allosteric ligands of human PBGS and, thus, identifies human PBGS as a medically relevant allosteric enzyme.