Grum-Tokars Valerie, Ratia Kiira, Begaye Adrian, Baker Susan C, Mesecar Andrew D
Center for Pharmaceutical Biotechnology and Department of Medicinal Chemistry and Pharmacognosy, University of Illinois, Chicago, IL 60607, United States.
Virus Res. 2008 Apr;133(1):63-73. doi: 10.1016/j.virusres.2007.02.015. Epub 2007 Mar 29.
Although the initial outbreaks of the deadly coronavirus that causes severe acute respiratory syndrome (SARS-CoV) were controlled by public health measures, the development of vaccines and antiviral agents for SARS-CoV is essential for improving control and treatment of future outbreaks. One potential target for SARS-CoV antiviral drug development is the 3C-like protease (3CLpro). This enzyme is an attractive target since it is essential for viral replication, and since there are now a number of high resolution X-ray structures of SARS-CoV 3CLpro available making structure-based drug-design possible. As a result, SARS-CoV 3CLpro has become the focus of numerous drug discovery efforts worldwide, but as a consequence, a variety of different 3CLpro expression constructs and kinetic assays have been independently developed making evaluation and comparison between potential inhibitors problematic. Here, we review the literature focusing on different SARS-CoV 3CLpro expression constructs and assays used to measure enzymatic activity. Moreover, we provide experimental evidence showing that the activity of 3CLpro enzymatic is significantly reduced when non-native sequences or affinity-tags are added to the N- or C-termini of the enzyme, or when the enzyme used in assays is at concentrations below the equilibrium dissociation constant of the 3CLpro dimer. We demonstrate for the first time the utility of a highly sensitive and novel Alexa488-QSY7 FRET-based peptide substrate designed for routine analysis and high-throughput screening, and show that kinetic constants determined from FRET-based assays that are uncorrected for inner-filter effects can lead to artifacts. Finally, we evaluated the effects of common assay components including DTT, NaCl, EDTA and DMSO on enzymatic activity, and we recommend standardized assay conditions and constructs for routine SARS-CoV 3CLpro assays to facilitate direct comparisons between SARS-CoV 3CLpro inhibitors under development worldwide.
尽管导致严重急性呼吸综合征（SARS-CoV）的致命冠状病毒的最初爆发通过公共卫生措施得到了控制，但开发针对SARS-CoV的疫苗和抗病毒药物对于改善未来疫情的控制和治疗至关重要。SARS-CoV抗病毒药物开发的一个潜在靶点是3C样蛋白酶（3CLpro）。这种酶是一个有吸引力的靶点，因为它对病毒复制至关重要，而且现在有许多SARS-CoV 3CLpro的高分辨率X射线结构，使得基于结构的药物设计成为可能。因此，SARS-CoV 3CLpro已成为全球众多药物研发工作的重点，但结果是，各种不同的3CLpro表达构建体和动力学测定方法已被独立开发出来，这使得对潜在抑制剂进行评估和比较变得困难。在这里，我们回顾了聚焦于不同SARS-CoV 3CLpro表达构建体以及用于测量酶活性的测定方法的文献。此外，我们提供了实验证据表明，当在该酶的N端或C端添加非天然序列或亲和标签时，或者当测定中使用的酶浓度低于3CLpro二聚体的平衡解离常数时，3CLpro酶的活性会显著降低。我们首次证明了一种专为常规分析和高通量筛选设计的基于Alexa488-QSY7荧光共振能量转移（FRET）的高灵敏度新型肽底物的实用性，并表明未经内滤效应校正的基于FRET的测定所确定的动力学常数可能会导致假象。最后，我们评估了常见测定成分（包括二硫苏糖醇、氯化钠、乙二胺四乙酸和二甲基亚砜）对酶活性的影响，并推荐用于常规SARS-CoV 3CLpro测定的标准化测定条件和构建体，以促进全球正在研发的SARS-CoV 3CLpro抑制剂之间的直接比较。
