Crystal Structure of Tryptophan Lyase (NosL): Evidence for Radical Formation at the Amino Group of Tryptophan
Crystal Structure of Tryptophan Lyase (NosL): Evidence for Radical Formation at the Amino Group of Tryptophan
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DOI：
10.1002/anie.201407320
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发表时间：
2014-10-27
影响因子：
16.6
通讯作者：
Fontecilla-Camps, Juan C.
中科院分区：
文献类型：
--
作者：
Nicolet, Yvain;Zeppieri, Laura;Fontecilla-Camps, Juan C.
精致链霉菌色氨酸裂解酶(NOSL)是一种自由基酶，催化合成3-甲基-2-吲哚酸，3-甲基-2-吲哚酸是合成抗生素诺西肽的前体。该反应涉及色氨酸Cα-Cβ键的断裂和吲哚环上氨基酸衍生的COOH片段的重组。本文报道了与其底物络合的NOSL的1.8埃分辨晶体结构。出人意料的是，只有一个色氨酸氨基氢原子被SAM衍生的5‘-脱氧腺苷自由基最佳地放置在H的抽提位置。这种取向反过来又排除了先前提出的离域吲哚自由基作为经历Cα-Cβ键断裂的物种。相反，立体化学的考虑表明，反应中间体是中心点NH色氨基。NosL与酪氨酸裂解酶ThiH和HydG的结构氨基酸序列比较强烈地表明，后两种酶中存在一个等效的中心点NH自由基。
Streptomyces actuosus tryptophan lyase (NosL) is a radical SAM enzyme which catalyzes the synthesis of 3-methyl-2-indolic acid, a precursor in the synthesis of the promising antibiotic nosiheptide. The reaction involves cleavage of the tryptophan C alpha-C beta bond and recombination of the amino-acid-derived -COOH fragment at the indole ring. Reported herein is the 1.8 angstrom resolution crystal structure of NosL complexed with its substrate. Unexpectedly, only one of the tryptophan amino hydrogen atoms is optimally placed for H abstraction by the SAM-derived 5'-deoxyadenosyl radical. This orientation, in turn, rules out the previously proposed delocalized indole radical as the species which undergoes C alpha-C beta bond cleavage. Instead, stereochemical considerations indicate that the reactive intermediate is a center dot NH tryptophanyl radical. A structure-based amino acid sequence comparison of NosL with the tyrosine lyases ThiH and HydG strongly suggests that an equivalent center dot NH radical operates in the latter enzymes.