Metabolism Department, WIL Research Laboratories, LLC, 1408 George Road, Ashland, OH 44805, USA.
Chem Biol Interact. 2010 Sep 6;187(1-3):370-2. doi: 10.1016/j.cbi.2010.01.039. Epub 2010 Feb 1.
Serum paraoxonase (PON1) is well recognized for its ability to hydrolyze arylesters, toxic oxon metabolites of organophosphate insecticides and nerve agents. PON1 is a member of gene family including also PON2 and PON3; however, the later two enzymes have very limited arylesterase and practically no organophosphatase activity. We have established that all three PONs are lactonases/lactonyzing enzymes with overlapping, but also distinct substrate specificity. Dihydrocoumarin (DHC), long chain fatty acid lactones and acylhomoserine lactones (AHLs) are hydrolyzed by all three PONs and likely represent their natural substrates. The 3D structure of PON1 is a six-bladed beta-propeller containing two Ca(2+) ions necessary for the enzyme stability and enzymatic activity. Senescence marker protein (SMP30), another putative six-bladed beta-propeller, hydrolyzes DFP, sarin and soman in the presence of Mg(2+) or Mn(2+). More recently, SMP30 was characterized as a gluconolactonase with a role in vitamin C metabolism. Bacterial phosphotriesterases (PTEs) are members of the amidohydrolase superfamily and differ in their structure from the eukaryotic organophosphatases; PTEs are (beta/alpha)(8) barrels with an active site containing two transition metal ions such as Co(2+), Mn(2+) or Zn(2+). PTE from Pseudomonas diminuta hydrolyzes paraoxon extremely efficiently; this enzyme was shown to hydrolyze also DHC and other lactones. At least 3 more bacterial lactonases, dubbed PTE-like lactonases (or PLL), have been identified to possess both lactonase and organophosphatase activities. Lactones are natural compounds, many of them with high biological activity, while organophosphates are human-made chemicals introduced in the 20th century. Thus, it is plausible that lactonase is the primary activity for which the enzymes discussed here evolved for, while the organophosphatase activity arose as a promiscuous activity during their evolution. Laboratory (directed) evolution studies provided mechanisms for their catalytic versatility and demonstrated experimentally the evolvability of promiscuous enzyme functions.
血清对氧磷酶（PON1）因其能够水解芳基酯的能力而广为人知，芳基酯是有机磷杀虫剂和神经毒剂的有毒氧代代谢物。PON1 是基因家族的一员，还包括 PON2 和 PON3；然而，后两种酶的芳基酯酶活性非常有限，几乎没有有机磷酸酶活性。我们已经确定，所有三种 PON 都是内酯酶/内酯酶，具有重叠但又不同的底物特异性。二氢香豆素（DHC）、长链脂肪酸内酯和酰基高丝氨酸内酯（AHLs）均可被三种 PON 水解，可能代表它们的天然底物。PON1 的 3D 结构是一个六叶β-螺旋桨，包含两个 Ca（2+）离子，这对于酶的稳定性和酶活性是必需的。衰老标志物蛋白（SMP30），另一种假定的六叶β-螺旋桨，在 Mg（2+）或 Mn（2+）存在下水解 DFP、沙林和梭曼。最近，SMP30 被表征为一种葡庚糖酸内酯酶，在维生素 C 代谢中发挥作用。细菌磷酸三酯酶（PTE）是酰胺水解酶超家族的成员，与真核有机磷酸酶在结构上有所不同；PTE 是（β/α）（8）桶，其活性位点包含两个过渡金属离子，如 Co（2+）、Mn（2+）或 Zn（2+）。来自苍白杆菌的 PTE 能够极其有效地水解对氧磷；该酶还被证明可以水解 DHC 和其他内酯。已经鉴定出至少 3 种其他细菌内酯酶，称为 PTE 样内酯酶（或 PLL），它们具有内酯酶和有机磷酸酶活性。内酯是天然化合物，其中许多具有很高的生物活性，而有机磷是 20 世纪人类制造的化学品。因此，可以合理地认为，内酯酶是这些酶进化的主要功能，而有机磷酸酶活性是在进化过程中产生的混杂活性。实验室（定向）进化研究为它们的催化多功能性提供了机制，并通过实验证明了混杂酶功能的可进化性。
