State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, China.
Nat Chem Biol. 2011 Mar;7(3):154-60. doi: 10.1038/nchembio.512. Epub 2011 Jan 16.
The radical S-adenosylmethionine (S-AdoMet) superfamily contains thousands of proteins that catalyze highly diverse conversions, most of which are poorly understood, owing to a lack of information regarding chemical products and radical-dependent transformations. We here report that NosL, involved in forming the indole side ring of the thiopeptide nosiheptide (NOS), is a radical S-AdoMet 3-methyl-2-indolic acid (MIA) synthase. NosL catalyzed an unprecedented carbon chain reconstitution of L-tryptophan to give MIA, showing removal of the Cα-N unit and shift of the carboxylate to the indole ring. Dissection of the enzymatic process upon the identification of products and a putative glycyl intermediate uncovered a radical-mediated, unusual fragmentation-recombination reaction. This finding unveiled a key step in radical S-AdoMet enzyme-catalyzed structural rearrangements during complex biotransformations. Additionally, NosL tolerated fluorinated L-tryptophan as the substrate, allowing for production of a regiospecifically halogenated thiopeptide that has not been found among the more than 80 members of the naturally occurring thiopeptide family.
激进的 S-腺苷甲硫氨酸（S-AdoMet）超家族包含数千种催化高度多样化转化的蛋白质，由于缺乏有关化学产物和自由基依赖性转化的信息，其中大多数转化仍未得到很好的理解。我们在这里报告说，参与形成噻唑肽 nosiheptide（NOS）吲哚侧环的 NosL 是一种激进的 S-AdoMet 3-甲基-2-吲哚酸（MIA）合酶。NosL 催化了前所未有的 L-色氨酸碳链重建，生成 MIA，显示出 Cα-N 单元的去除和羧酸盐向吲哚环的转移。在鉴定产物和假定的甘氨酰中间物的基础上对酶促过程进行剖析，揭示了一种由自由基介导的不寻常的片段-重组反应。这一发现揭示了在复杂生物转化过程中，自由基 S-AdoMet 酶催化的结构重排的关键步骤。此外，NosL 可以容忍氟代 L-色氨酸作为底物，从而可以生产出一种区域特异性卤代噻唑肽，而在超过 80 种天然存在的噻唑肽家族成员中尚未发现这种肽。
