β-Amyrin synthase (bAS) is a representative plant oxidosqualene cyclase (OSC), and previous studies have identified many functional residues and mutants that can alter its catalytic activity. However, the regulatory mechanism of the active site architecture for adjusting the catalytic activity remains unclear. In this study, we investigate the function of key residues and their regulatory effects on the catalytic activity of Glycyrrhiza glabra β-amyrin synthase (GgbAS) through molecular dynamics simulations and site-directed mutagenesis experiments. We identified the plasticity residues located in two active site regions and explored the interactions between these residues and tetracyclic/pentacyclic intermediates. Based on computational and experimental results, we further categorize these plasticity residues into three types: effector, adjuster, and supporter residues, according to their functions in the catalytic process. This study provides valuable insights into the catalytic mechanism and active site plasticity of GgbAS, offering important references for the rational enzyme engineering of other OSC enzyme.

中文翻译：

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利用活性位点的可塑性残基调节 β-香树脂醇合酶 GgBAS 的催化活性

β-香树脂合酶（bAS）是一种代表性的植物氧化角鲨烯环化酶（OSC），之前的研究已经鉴定出许多可以改变其催化活性的功能残基和突变体。然而，调节催化活性的活性位点结构的调节机制仍不清楚。在本研究中，我们通过分子动力学模拟和定点诱变实验研究了关键残基的功能及其对光果甘草β-香树脂合酶（GgbAS）催化活性的调节作用。我们鉴定了位于两个活性位点区域的可塑性残基，并探索了这些残基与四环/五环中间体之间的相互作用。基于计算和实验结果，我们根据其在催化过程中的功能，进一步将这些可塑性残基分为三类：效应子残基、调节子残基和支持残基。该研究为GgbAS的催化机制和活性位点可塑性提供了有价值的见解，为其他OSC酶的合理酶工程提供了重要参考。