Three-dimensional structure of DesVI from Streptomyces venezuelae:: A sugar N,N-dimethyltransferase required for dTDP-desosamine biosynthesis
Three-dimensional structure of DesVI from Streptomyces venezuelae:: A sugar N,N-dimethyltransferase required for dTDP-desosamine biosynthesis
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DOI：
10.1021/bi800063j
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发表时间：
2008-04-01
期刊：
影响因子：
2.9
通讯作者：
Holden, Hazel M.
中科院分区：
文献类型：
--
作者：
Burgie, E. Sethe;Holden, Hazel M.
D-Desosamine或3-（二甲氨基）-3，4，6-三脱氧葡萄糖是在大环内酯类抗生素红霉素中发现的一种不寻常的糖，它已被证明在药物的生物活性中发挥关键作用。通过利用dTDP-desosamine作为其底物的糖基转移酶的作用，将Desosamine添加到母体糖苷配基中。委内瑞拉链霉菌中dTDP-desosamine的生物合成需要六种酶，最后一步由DesVI催化，DesVI是一种N，N-二甲基转移酶。在这里，我们描述的X-射线晶体结构确定为2.0 A分辨率的DesVI与S-腺苷甲硫氨酸（SAM）和底物类似物UDP-苯络合。DesVI二聚体的每个亚基含有七链混合β-折叠，两侧为α-螺旋。除了这个主要的三级结构元件，还有一个四链反平行β-折叠，为亚基-亚基组装提供了必要的平台。在UDP-苯结合模式的基础上，DesVI底物dTDP-3-（甲氨基）-3，4，6-三脱氧葡萄糖已被建模为活性位点。该模型将糖的C-6'甲基基团置于疏水补丁中，该疏水补丁在推定的核苷酸连接的糖二甲基转移酶中是非常保守的。它由Trp 140，Met 178和Ile 200组成。糖的C-2'羟基位于Tyr 14附近，并且其C-3'氨基被适当地定位用于直接在线攻击辅因子的反应性甲基。虽然催化碳、氧、硫和氮的单烷基化的甲基转移酶已经被很好地表征，但是关于能够进行N，N-二甲基化反应的酶知之甚少。因此，本文报道的DesVI的三元结构可作为一个新的二甲基转移酶家族的结构范例，该家族在核苷酸连接的糖上发挥作用。
D-Desosamine, or 3-(dimethylamino)-3,4,6-trideoxyglucose, is an unusual sugar found on the macrolide antibiotic erythromycin, and it has been shown to play a critical role in the biological activity of the drug. Desosamine is added to the parent aglycone via the action of a glycosyltransferase that utilizes dTDP-desosamine as its substrate. Six enzymes are required for the biosynthesis of dTDP-desosamine in Streptomyces venezuelae, with the last step catalyzed by DesVI, an N,N-dimethyltransferase. Here we describe the X-ray crystal structure determined to 2.0 A resolution of DesVI complexed with S-adenosylmethionine (SAM) and the substrate analogue UDP-benzene. Each subunit of the DesVI dimer contains a seven-stranded mixed beta-sheet flanked on either side by alpha-helices. In addition to this major tertiary structural element, there is a four-stranded antiparallel beta-sheet that provides the platform necessary for subunit-subunit assembly. On the basis of the UDP-benzene binding mode, the DesVI substrate, dTDP-3-(methylamino)-3,4,6-trideoxyglucose, has been modeled into the active site. This model places the C-6' methyl group of the sugar into a hydrophobic patch that is well-conserved among putative nucleotide-linked sugar dimethyltransferases. It is formed by Trp 140, Met 178, and Ile 200. The sugar C-2' hydroxyl sits near Tyr 14, and its C-3' amino group is properly positioned for direct in-line attack of the cofactor's reactive methyl group. While methyltransferases that catalyze single alkylations at carbons, oxygens, sulfurs, and nitrogens have been well characterized, little is known regarding enzymes capable of N,N-dimethylation reactions. As such, the ternary structure of DesVI reported here serves as a structural paradigm for a new family of dimethyltransferases that function on nucleotide-linked sugars.