Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000, Grenoble, France.
Univ. Grenoble Alpes, CEA, CNRS, IRIG-DIESE-SyMMES-CAMPE, 38000, Grenoble, France.
Nat Commun. 2022 Apr 27;13(1):2284. doi: 10.1038/s41467-022-29980-4.
2-iminoacetate synthase ThiH is a radical S-adenosyl-L-methionine (SAM) L-tyrosine lyase and catalyzes the L-tyrosine Cα-Cβ bond break to produce dehydroglycine and p-cresol while the radical SAM L-tryptophan lyase NosL cleaves the L-tryptophan Cα-C bond to produce 3-methylindole-2-carboxylic acid. It has been difficult to understand the features that condition one C-C bond break over the other one because the two enzymes display significant primary structure similarities and presumably similar substrate-binding modes. Here, we report the crystal structure of L-tyrosine bound ThiH from Thermosinus carboxydivorans revealing an unusual protonation state of L-tyrosine upon binding. Structural comparison of ThiH with NosL and computational studies of the respective reactions they catalyze show that substrate activation is eased by tunneling effect and that subtle structural changes between the two enzymes affect, in particular, the hydrogen-atom abstraction by the 5´-deoxyadenosyl radical species, driving the difference in reaction specificity.
2-亚氨基乙酸合酶 ThiH 是一种自由基 S-腺苷甲硫氨酸（SAM）L-酪氨酸裂解酶，催化 L-酪氨酸 Cα-Cβ 键断裂，生成脱水甘氨酸和对甲酚，而自由基 SAM L-色氨酸裂解酶 NosL 则催化 L-色氨酸 Cα-C 键断裂，生成 3-甲基吲哚-2-羧酸。由于这两种酶具有显著的一级结构相似性，并且可能具有相似的底物结合模式，因此很难理解导致一个 C-C 键断裂而不是另一个 C-C 键断裂的特征。在这里，我们报道了来自 Thermosinus carboxydivorans 的 L-酪氨酸结合 ThiH 的晶体结构，揭示了结合时 L-酪氨酸的异常质子化状态。将 ThiH 与 NosL 进行结构比较，并对它们催化的反应进行计算研究表明，隧道效应缓解了底物的活化，而两种酶之间的细微结构变化，特别是影响 5´-脱氧腺苷自由基物种的氢原子提取，从而导致反应特异性的差异。
