Synthesis of N-acetyl-d-quinovosamine in Rhizobium etli CE3 is completed after its 4-keto-precursor is linked to a carrier lipid.
Synthesis of N-acetyl-d-quinovosamine in Rhizobium etli CE3 is completed after its 4-keto-precursor is linked to a carrier lipid.
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在根瘤菌 CE3 中，N-乙酰基-d-喹诺糖胺的合成在其 4-酮前体与载体脂质连接后完成。
DOI：
10.1099/mic.0.000576
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Noel,KDale
中科院分区：
文献类型：
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作者：
Li,Tiezheng;Noel,KDale
细菌O-抗原是在脂类载体上合成的，然后被转移到脂多糖的核心结构上。根瘤菌等CE3脂多糖是一个了解O-抗原生物学功能的模型。CE3O-抗原的结构和遗传学是已知的。然而，已提出的用于CE3O-抗原合成的酶学研究在体外很少被检验，甚至添加糖开始合成也是不确定的。一个基于诱变研究的模型预测，2-乙酰氨基-2，6-二脱氧-d-葡萄糖(Quinac)是第一个O-抗原糖，而基因wreV和wreQandwreU指导Quinac的合成和O-抗原的启动。以前，UDP-Quinac的合成是在WreV(4，6-己糖脱水酶)和WreQ(4-还原酶)的体外催化下进行的，但在这一传统的脱氧己糖合成途径中，WreQ的催化速度非常慢。在体外检测了WreU转移酶的活性后，本研究解释了这一表面上的缺陷。结果符合WreU将糖-1-磷酸转移到磷酸杆菌(BPP)以启动O-抗原合成的预测。有趣的是，使用WreV催化产物[UDP-4-酮-6-脱氧-GlcNAc(UDP-KdgNAc)]作为糖磷供体的WreU表现出比使用UDP-Quinac高得多的活性。此外，以WreU产生的BPPP-KdgNAc为底物的WreQ催化比以UDP-KdgNAc为底物的催化速度快几个数量级。推测的产物BPPP-Quinac作为受体底物在Anin体外试验中添加第二O-抗原糖甘露糖。这些结果暗示了一种新的合成6-脱氧己糖的途径，当Quinac是多糖或寡糖重复单元的第一糖时，细菌通常利用该途径：udp-GlcNAc→udp-kdgNAc→bppp-kdgNAc→bppp-quinac。
Bacterial O-antigens are synthesized on lipid carriers before being transferred to lipopolysaccharide core structures.Rhizobium etliCE3 lipopolysaccharide is a model for understanding O-antigen biological function. CE3 O-antigen structure and genetics are known. However, proposed enzymology for CE3 O-antigen synthesis has been examined very littlein vitro, and even the sugar added to begin the synthesis is uncertain. A model based on mutagenesis studies predicts that 2-acetamido-2,6-dideoxy-d-glucose (QuiNAc) is the first O-antigen sugar and that geneswreV, wreQandwreUdirect QuiNAc synthesis and O-antigen initiation. Previously, synthesis of UDP-QuiNAc was shown to occurin vitrowith a WreV orthologue (4,6-hexose dehydratase) and WreQ (4-reductase), but the WreQ catalysis in this conventional deoxyhexose-synthesis pathway was very slow. This seeming deficiency was explained in the present study after WreU transferase activity was examinedin vitro.Results fit the prediction that WreU transfers sugar-1-phosphate to bactoprenyl phosphate (BpP) to initiate O-antigen synthesis. Interestingly, WreU demonstrated much higher activity using the product of the WreV catalysis [UDP-4-keto-6-deoxy-GlcNAc (UDP-KdgNAc)] as the sugar-phosphate donor than using UDP-QuiNAc. Furthermore, the WreQ catalysis with WreU-generated BpPP-KdgNAc as the substrate was orders of magnitude faster than with UDP-KdgNAc. The inferred product BpPP-QuiNAc reacted as an acceptor substrate in anin vitroassay for addition of the second O-antigen sugar, mannose. These results imply a novel pathway for 6-deoxyhexose synthesis that may be commonly utilized by bacteria when QuiNAc is the first sugar of a polysaccharide or oligosaccharide repeat unit: UDP-GlcNAc → UDP-KdgNAc → BpPP-KdgNAc → BpPP-QuiNAc.