Key Laboratory of Urban Environment and Health, Institute of Urban Environment , Chinese Academy of Sciences , Xiamen 361021 , China.
Institute of Chemistry, NAWI Graz , University of Graz , Graz 8010 , Austria.
Environ Sci Technol. 2019 Jan 15;53(2):634-641. doi: 10.1021/acs.est.8b04389. Epub 2018 Dec 24.
Arsenosugars are arsenic-containing ribosides that play a substantial role in arsenic biogeochemical cycles. Arsenosugars were identified more than 30 years ago, and yet their mechanism of biosynthesis remains unknown. In this study we report identification of the arsS gene from the cyanobacterium Synechocystis sp. PCC 6803 and show that it is involved in arsenosugar biosynthesis. In the Synechocystis sp. PCC 6803 ars operon, arsS is adjacent to the arsM gene that encodes an As(III) S-adenosylmethionine (SAM) methyltransferase. The gene product, ArsS, contains a characteristic CXCXC motif which is typical for the radical SAM superfamily. The function of ArsS was identified from a combination of arsS disruption in Synechocystis sp. PCC 6803 and heterologous expression of arsM and arsS in Escherichia coli. Both genes are necessary, indicating a multistep pathway of arsenosugar biosynthesis. In addition, we demonstrate that ArsS orthologs from three other freshwater cyanobacteria and one picocyanobacterium are involved in arsenosugar biosynthesis in those microbes. This study represents the identification of the first two steps in the pathway of arsenosugar biosynthesis. Our discovery expands the catalytic repertoire of the diverse radical SAM enzyme superfamily and provides a basis for studying the biogeochemistry of complex organoarsenicals.
砷糖是含有砷的核苷，在砷的生物地球化学循环中起着重要作用。砷糖早在 30 多年前就被发现了，但它们的生物合成机制仍不清楚。在这项研究中，我们从蓝藻集胞藻 PCC 6803 中鉴定出了 arsS 基因，并证实它参与了砷糖的生物合成。在集胞藻 PCC 6803 的 ars 操纵子中，arsS 与编码 As(III) S-腺苷甲硫氨酸（SAM）甲基转移酶的 arsM 基因相邻。 ArsS 的产物包含一个特征性的 CXCXC 基序，这是典型的自由基 SAM 超家族。 ArsS 的功能是通过集胞藻 PCC 6803 中 arsS 的破坏和大肠杆菌中 arsM 和 arsS 的异源表达相结合来确定的。这两个基因都是必需的，这表明砷糖的生物合成是一个多步骤的途径。此外，我们证明了来自其他三种淡水蓝藻和一种微藻的 ArsS 同源物参与了这些微生物中砷糖的生物合成。这项研究代表了砷糖生物合成途径的前两个步骤的鉴定。我们的发现扩展了不同的自由基 SAM 酶超家族的催化谱，并为研究复杂有机砷的生物地球化学提供了基础。
