Flavin adenine dinucleotide-dependent 4-phospho-D-erythronate dehydrogenase is responsible for the 4-phosphohydroxy-L-threonine pathway in vitamin B6 biosynthesis in Sinorhizobium meliloti
Flavin adenine dinucleotide-dependent 4-phospho-D-erythronate dehydrogenase is responsible for the 4-phosphohydroxy-L-threonine pathway in vitamin B6 biosynthesis in Sinorhizobium meliloti
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DOI：
10.1128/jb.01999-05
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发表时间：
2006-07-01
影响因子：
3.2
通讯作者：
Hoshino, Tatsuo
中科院分区：
文献类型：
--
作者：
Tazoe, Masaaki;Ichikawa, Keiko;Hoshino, Tatsuo
苜蓿中华根瘤菌（Sinorhizobium meliloti）中维生素B-6的生物合成途径与大肠杆菌K-12中的相似;在两种生物中，该途径包括两个中间体1-脱氧-D-木酮糖5-磷酸和4-磷酸羟基-L-苏氨酸（4-PHT）的缩合。在这里，我们报告了一个基因命名为pdxR的功能对应于pdxB基因的E。大肠杆菌中表达，编码一个染料连接的黄素腺嘌呤二核苷酸依赖性4-磷酸-D-精氨酸（4PE）脱氢酶。该酶催化4PE氧化为3-羟基-4-磷酸羟基-α-酮丁酸，并且在辅因子需求方面与大肠杆菌pdxB基因产物明显不同。大肠杆菌，这是已知的NAD依赖性酶。以前，我们发现，在S。苜蓿IFO 14782，4PHT由4-羟基-L-苏氨酸合成，并且该合成从乙醇醛和甘氨酸开始。然而，在本研究中，我们在S.苜蓿草苷完全来源于乙醇醛（主要途径）。基于4PE在4PHT途径中的参与，使用C-13核磁共振光谱检查了不同样品的C-13标记的乙醇醛掺入吡哆醇分子中。基于光谱分析，推测乙醇醛合成4-PHT的过程包括以下步骤：乙醇醛依次通过转酮醇酶、激酶和异构酶代谢为D-赤藓酮糖、D-赤藓酮糖4-磷酸和D-赤藓糖4-磷酸，然后通过E.大肠杆菌，虽然催化前两步的酶的作用机制是不同的。
The vitamin B-6 biosynthetic pathway in Sinorhizobium meliloti is similar to that in Escherichia coli K-12; in both organisms this pathway includes condensation of two intermediates, 1-deoxy-D-xylulose 5-phosphate and 4-phosphohydroXy-L-threonine (4PHT). Here, we report cloning of a gene designated pdxR that functionally corresponds to the pdxB gene of E. coli and encodes a dye-linked flavin adenine dinucleotide-dependent 4-phospho-D-erythronate (4PE) dehydrogenase. This enzyme catalyzes the oxidation of 4PE to 3-hydroxy-4-phosphohydroxy-alpha-ketobutyrate and is clearly different in terms of cofactor requirements from the pdxB gene product of E. coli, which is known to be an NAD-dependent enzyme. Previously, we revealed that in S. meliloti IFO 14782, 4PHT is synthesized from 4-hydroxy-L-threonine and that this synthesis starts with glycolaldehyde and glycine. However, in this study, we identified a second 4PHT pathway in S. meliloti that originates exclusively from glycolaldehyde (the major pathway). Based on the involvement of 4PE in the 4PHT pathway, the incorporation of different samples of C-13-labeled glycolaldehyde into pyridoxine molecules was examined using C-13 nuclear magnetic resonance spectroscopy. On the basis of the spectral analyses, the synthesis of 4PHT from glycolaldehyde was hypothesized to involve the following steps: glycolaldehyde is sequentially metabolized to D-erythrulose, D-erythrulose 4-phosphate, and D-erythrose 4-phosphate by transketolase, kinase, and isomerase, respectively; and D-erythrose 4-phosphate is then converted to 4PHT by the conventional three-step pathway elucidated in E. coli, although the mechanism of action of the enzymes catalyzing the first two steps is different.