Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
Department of Chemistry, The Pennsylvania State University, University Park, PA, USA.
Nature. 2019 Feb;566(7742):94-99. doi: 10.1038/s41586-019-0894-z. Epub 2019 Feb 6.
Small molecules containing the N-nitroso group, such as the bacterial natural product streptozotocin, are prominent carcinogens and important cancer chemotherapeutics. Despite the considerable importance of this functional group to human health, enzymes dedicated to the assembly of the N-nitroso unit have not been identified. Here we show that SznF, a metalloenzyme from the biosynthesis of streptozotocin, catalyses an oxidative rearrangement of the guanidine group of N-methyl-L-arginine to generate an N-nitrosourea product. Structural characterization and mutagenesis of SznF reveal two separate active sites that promote distinct steps in this transformation using different iron-containing metallocofactors. This biosynthetic reaction, which has little precedent in enzymology or organic synthesis, expands the catalytic capabilities of non-haem-iron-dependent enzymes to include N-N bond formation. We find that biosynthetic gene clusters that encode SznF homologues are widely distributed among bacteria-including environmental organisms, plant symbionts and human pathogens-which suggests an unexpectedly diverse and uncharacterized microbial reservoir of bioactive N-nitroso metabolites.
含有 N-亚硝基基团的小分子，如细菌天然产物链脲佐菌素，是重要的致癌物质和癌症化疗药物。尽管这个官能团对人类健康非常重要，但目前尚未鉴定出专门用于组装 N-亚硝基单元的酶。在这里，我们展示了 SznF，一种来自链脲佐菌素生物合成的金属酶，催化 N-甲基-L-精氨酸胍基的氧化重排，生成 N-亚硝脲产物。通过对 SznF 的结构表征和突变分析，揭示了两个独立的活性位点，使用不同含铁金属辅因子促进了这一转化的不同步骤。这种生物合成反应在酶学或有机合成中鲜有先例，它扩展了非血红素铁依赖性酶的催化能力，包括 N-N 键的形成。我们发现，编码 SznF 同源物的生物合成基因簇广泛分布于细菌中，包括环境生物、植物共生体和人类病原体，这表明微生物中存在着丰富多样且尚未被认识的生物活性 N-亚硝基代谢物库。
