Substrate Analogues for the Enzyme-Catalyzed Detoxification of the Organophosphate Nerve Agents—Sarin, Soman, and Cyclosarin
作者:Andrew N. Bigley、Steven P. Harvey、Tamari Narindoshvili、Frank M. Raushel
DOI:10.1021/acs.biochem.1c00361
日期:2021.9.28
The G-type nerve agents, sarin (GB), soman (GD), and cyclosarin (GF), are among the most toxic compounds known. Much progress has been made in evolving the enzyme phosphotriesterase (PTE) from Pseudomonas diminuta for the decontamination of the G-agents; however, the extreme toxicity of the G-agents makes the use of substrate analogues necessary. Typical analogues utilize a chromogenic leaving group to facilitate high-throughput screening, and substitution of an O-methyl for the P-methyl group found in the G-agents, in an effort to reduce toxicity. Till date, there has been no systematic evaluation of the effects of these substitutions on catalytic activity, and the presumed reduction in toxicity has not been tested. A series of 21 G-agent analogues, including all combinations of O-methyl, p-nitrophenyl, and thiophosphate substitutions, have been synthesized and evaluated for their ability to unveil the stereoselectivity and catalytic activity of PTE variants against the authentic G-type nerve agents. The potential toxicity of these analogues was evaluated by measuring the rate of inactivation of acetylcholinesterase (AChE). All of the substitutions reduced inactivation of AChE by more than 100-fold, with the most effective being the thiophosphate analogues, which reduced the rate of inactivation by about 4–5 orders of magnitude. The analogues were found to reliably predict changes in catalytic activity and stereoselectivity of the PTE variants and led to the identification of the BHR-30 variant, which has no apparent stereoselectivity against GD and a kcat/Km of 1.4 × 106, making it the most efficient enzyme for GD decontamination reported till date.
G型神经毒剂,包括沙林(GB)、梭曼(GD)和环沙林(GF),是已知毒性最强的化合物之一。在利用铜绿假单胞菌的磷酸三酯酶(PTE)进化以去除G型毒剂方面已经取得了很大进展;然而,G型毒剂的极高毒性使得使用底物类似物成为必要。典型的类似物采用色原性离去基团以促进高通量筛选,并通过用O-甲基取代G型毒剂中的P-甲基,以期降低毒性。迄今为止,尚未对这些取代基对催化活性的影响进行系统评估,并且所推测的毒性降低尚未得到验证。合成了一系列21种G型毒剂类似物,包括所有O-甲基、对硝基苯基和硫代磷酸酯取代基的组合,并评估了它们揭示PTE变体对实际G型神经毒剂的立体选择性和催化活性的能力。通过测定乙酰胆碱酯酶(AChE)的失活速率,评估了这些类似物的潜在毒性。所有取代基使AChE失活减缓了100倍以上,其中最有效的是硫代磷酸酯类似物,其使失活速率降低了约4-5个数量级。发现这些类似物可准确预测催化活性和立体选择性的变化,并有助于鉴定出BHR-30变体,该变体对GD没有明显的立体选择性,且kcat/Km值为1.4 × 106,使其成为迄今为止报道的用于GD去除的最有效的酶。