Faculty of Biology, University of Freiburg, Freiburg, Germany.
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, USA.
Nat Chem Biol. 2020 May;16(5):556-563. doi: 10.1038/s41589-020-0476-2. Epub 2020 Feb 17.
One of the hallmark reactions catalyzed by flavin-dependent enzymes is the incorporation of an oxygen atom derived from dioxygen into organic substrates. For many decades, these flavin monooxygenases were assumed to use exclusively the flavin-C4a-(hydro)peroxide as their oxygen-transferring intermediate. We demonstrate that flavoenzymes may instead employ a flavin-N5-peroxide as a soft α-nucleophile for catalysis, which enables chemistry not accessible to canonical monooxygenases. This includes, for example, the redox-neutral cleavage of carbon-hetero bonds or the dehalogenation of inert environmental pollutants via atypical oxygenations. We furthermore identify a shared structural motif for dioxygen activation and N5-functionalization, suggesting a conserved pathway that may be operative in numerous characterized and uncharacterized flavoenzymes from diverse organisms. Our findings show that overlooked flavin-N5-oxygen adducts are more widespread and may facilitate versatile chemistry, thus upending the notion that flavin monooxygenases exclusively function as nature's equivalents to organic peroxides in synthetic chemistry.
黄素依赖酶催化的标志性反应之一是将氧原子从分子氧掺入有机底物中。几十年来，这些黄素单加氧酶被认为仅使用黄素-C4a-（氢）过氧化物作为其氧转移中间体。我们证明，黄素酶可能转而将黄素-N5-过氧化物用作催化的软 α-亲核试剂，从而使典型单加氧酶无法进行的化学反应成为可能。这包括例如，通过非典型氧化作用使碳杂键发生氧化还原中性裂解或使惰性环境污染物脱卤。此外，我们还确定了用于分子氧活化和 N5-官能化的共享结构基序，表明存在一种保守的途径，该途径可能在来自不同生物体的许多已鉴定和未鉴定的黄素酶中起作用。我们的发现表明，被忽视的黄素-N5-氧加合物更为普遍，并且可能促进多功能化学，从而颠覆了这样一种观念，即黄素单加氧酶仅作为合成化学中有机过氧化物的等效物在自然界中起作用。
