Propanediol dehydratase (PD), a recently characterized member of the glycyl radical enzyme (GRE) family, uses protein-based radicals to catalyze the chemically challenging dehydration of (S)-1,2-propanediol. This transformation is also performed by the well-studied enzyme B₁₂-dependent propanediol dehydratase (B₁₂-PD) using an adenosylcobalamin cofactor. Despite the prominence of PD in anaerobic microorganisms, it remains unclear if the mechanism of this enzyme is similar to that of B₁₂-PD. Here we report ¹⁸O labeling experiments that suggest PD and B₁₂-PD employ distinct mechanisms. Unlike B₁₂-PD, PD appears to catalyze the direct elimination of a hydroxyl group from an initially formed substrate-based radical, avoiding the generation of a 1,1-gem diol intermediate. Our studies provide further insights into how GREs perform elimination chemistry and highlight how nature has evolved diverse strategies for catalyzing challenging reactions.

中文翻译：

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1,2-丙二醇脱水酶的表征揭示了B ₁₂依赖性和糖基自由基酶的不同机制。

丙二醇脱水酶（PD）是糖基自由基酶（GRE）家族中最近被表征的成员，它使用基于蛋白质的自由基来催化化学上具有挑战性的（S）-1,2-丙二醇脱水。还使用腺苷钴胺素辅因子，通过充分研究的酶B ₁₂依赖性丙二醇脱水酶（B ₁₂ -PD）来执行此转化。尽管PD在厌氧微生物中占主导地位，但尚不清楚该酶的机制是否与B ₁₂ -PD相似。在这里，我们报告¹⁸ O标记实验，表明PD和B ₁₂ -PD采用不同的机制。不像B ₁₂-PD，PD似乎催化了从最初形成的基于底物的自由基中直接消除羟基，从而避免了1,1-宝石二醇中间体的产生。我们的研究为GRE如何执行消除化学反应提供了进一步的见解，并强调了自然界如何发展出多种策略来催化具有挑战性的反应。