The exciting discovery of the giant DNA Mimivirus in 2003 challenged the conventional description of viruses in a radical way, and since then, dozens of additional giant viruses have been identified. It has now been demonstrated that the Mimivirus genome encodes for the two enzymes required for the production of the unusual sugar 4-amino-4,6-dideoxy-d-glucose, namely a 4,6-dehydratase and an aminotransferase. In light of our long-standing interest in the bacterial 4,6-dehydratases and in unusual sugars in general, we conducted a combined structural and functional analysis of the Mimivirus 4,6-dehydratase referred to as R141. For this investigation, the three-dimensional X-ray structure of R141 was determined to 2.05 Å resolution and refined to an R-factor of 18.3%. The overall fold of R141 places it into the short-chain dehydrogenase/reductase (SDR) superfamily of proteins. Whereas its molecular architecture is similar to that observed for the bacterial 4,6-dehydratases, there are two key regions where the polypeptide chain adopts different conformations. In particular, the conserved tyrosine that has been implicated as a catalytic acid or base in SDR superfamily members is splayed away from the active site by nearly 12 Å, thereby suggesting that a major conformational change must occur upon substrate binding. In addition to the structural analysis, the kinetic parameters for R141 using either dTDP-d-glucose or UDP-d-glucose as substrates were determined. Contrary to a previous report, R141 demonstrates nearly identical catalytic efficiency with either nucleotide-linked sugar. The data presented herein represent the first three-dimensional model for a viral 4,6-dehydratase and thus expands our understanding of these fascinating enzymes.

中文翻译：

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棘阿米巴多噬性拟南芥糖的4,6-脱水糖的生化分析。

2003年巨人DNA Mimivirus的激动人心的发现从根本上挑战了病毒的传统描述，此后，又发现了数十种其他巨人病毒。现已证明，拟病毒基因组编码产生非常规糖4-氨基-4，6-二脱氧-d-葡萄糖所需的两种酶，即4，6-脱水酶和氨基转移酶。鉴于我们长期以来对细菌4,6-脱水酶和不寻常的糖具有浓厚兴趣，我们对称为R141的拟病毒4,6-脱水酶进行了结构和功能分析。为了进行这项研究，确定了R141的三维X射线结构为2.05Å分辨率，并细化为R因子18.3％。R141的整体折叠使其成为蛋白质的短链脱氢酶/还原酶（SDR）超家族。尽管其分子结构与细菌4,6-脱水酶相似，但多肽链有两个关键区域具有不同构象。特别是，已被暗示为SDR超家族成员中的催化酸或碱的保守酪氨酸从活性位点扩展了将近12，从而表明在结合底物时必须发生主要的构象变化。除了结构分析之外，还确定了使用dTDP-d-葡萄糖或UDP-d-葡萄糖作为底物的R141的动力学参数。与以前的报告相反，R141证明了与任一核苷酸连接的糖几乎相同的催化效率。