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标题：CO synthesized from the central one-carbon pool as source for the iron carbonyl in O2-tolerant [NiFe]-hydrogenase
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作者：Ingmar Bürstel ; Elisabeth Siebert ; Stefan Frielingsdorf 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：51
页码：14722-14726
DOI：10.1073/pnas.1614656113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceActivation of dihydrogen is by far not a trivial catalytic reaction. Microbes have evolved sophisticated hydrogenases with complex transition metal centers to get access to H2. A recurring feature of these centers is the presence of iron atoms equipped with carbon monoxide ligands. In case of [NiFe]-hydrogenases, which contain a NiFe(CN)2CO catalytic center, biosynthesis of the toxic CO ligand remained elusive. We show that [NiFe]-hydrogenases that are catalytically active in the presence of dioxygen use a dedicated maturase for CO ligand synthesis under aerobic conditions. CO is derived from the most oxidized intermediate of the central one-carbon metabolism, formyl-tetrahydrofolate. This discovery contributes a so far unknown reaction to the one-carbon metabolism and opens perspectives for chemical and of bioinspired catalysis. Hydrogenases are natures key catalysts involved in both microbial consumption and production of molecular hydrogen. H2 exhibits a strongly bonded, almost inert electron pair and requires transition metals for activation. Consequently, all hydrogenases are metalloenzymes that contain at least one iron atom in the catalytic center. For appropriate interaction with H2, the iron moiety demands for a sophisticated coordination environment that cannot be provided just by standard amino acids. This dilemma has been overcome by the introduction of unprecedented chemistry--that is, by ligating the iron with carbon monoxide (CO) and cyanide (or equivalent) groups. These ligands are both unprecedented in microbial metabolism and, in their free form, highly toxic to living organisms. Therefore, the formation of the diatomic ligands relies on dedicated biosynthesis pathways. So far, biosynthesis of the CO ligand in [NiFe]-hydrogenases was unknown. Here we show that the aerobic H2 oxidizer Ralstonia eutropha, which produces active [NiFe]-hydrogenases in the presence of O2, employs the auxiliary protein HypX (hydrogenase pleiotropic maturation X) for CO ligand formation. Using genetic engineering and isotope labeling experiments in combination with infrared spectroscopic investigations, we demonstrate that the -carbon of glycine ends up in the CO ligand of [NiFe]-hydrogenase. The -carbon of glycine is a building block of the central one-carbon metabolism intermediate, N10-formyl-tetrahydrofolate (N10-CHO-THF). Evidence is presented that the multidomain protein, HypX, converts the formyl group of N10-CHO-THF into water and CO, thereby providing the carbonyl ligand for hydrogenase. This study contributes insights into microbial biosynthesis of metal carbonyls involving toxic intermediates.
关键词：hydrogenase ; metalloenzyme ; carbonyl ligand ; formyl-THF ; one-carbon metabolism