Roles and regulation of the glutamate racemase isogenes, racE and yrpC, in Bacillus subtilis
Roles and regulation of the glutamate racemase isogenes, racE and yrpC, in Bacillus subtilis
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DOI：
10.1099/mic.0.27045-0
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发表时间：
2004-09-01
期刊：
影响因子：
2.8
通讯作者：
Itoh, Y
中科院分区：
文献类型：
--
作者：
Kimura, K;Tran, LSP;Itoh, Y
包括大肠杆菌在内的许多细菌都有一个编码谷氨酸消旋酶的独特基因。这种酶催化D-戊二酸的形成，这是细胞壁肽聚糖合成所必需的。然而，枯草芽孢杆菌具有两个谷氨酸消旋酶基因，命名为racE和yrpC。由于racE似乎是在丰富的培养基中生长所不可或缺的，yrpC在D-氨基酸合成中的作用是模糊的。racE-和yrpC-敲除突变体的实验证实，racE是在丰富的培养基中生长所必需的，但表明该基因在基本培养基中生长是不稳定的，其中yrpC执行racE的回补作用。LacZ融合试验表明，racE在两种类型的培养基中表达，但yrpC仅在基本培养基中表达，这解释了丰富培养基中yrpC功能的缺失。对于B，racE和yrpC都不是必需的。枯草杆菌细胞合成聚-γ-DL-谷氨酸（γ-PGA），一种通过γ-羧酰胺键连接的D-和L-谷氨酸的胶囊多肽。野生型细胞降解胶囊在后期稳定期，而不积累的降解产物，D-谷氨酸和L-谷氨酸，在培养基中。相反，racE或yrpC突变细胞积累了大量的D-谷氨酸，但没有L-谷氨酸。外源D-谷氨酸的利用在突变体中有一定的缺陷，racE和yrpC的双突变严重损害了D-氨基酸的利用。因此，这两种消旋酶基因似乎是完成从γ-PGA产生的外源D-谷氨酸的催化所必需的。
Many bacteria, including Escherichia coli, have a unique gene that encodes glutamate racemase. This enzyme catalyses the formation of D-glutarnate, which is necessary for cell wall pepticloglycan synthesis. However, Bacillus subtilis has two glutamate racemase genes, named racE and yrpC. Since racE appears to be indispensable for growth in rich medium, the role of yrpC in D-amino acid synthesis is vague. Experiments with racE- and yrpC-knockout mutants confirmed that racE is essential for growth in rich medium but showed that this gene was dispensable for growth in minimal medium, where yrpC executes the anaplerotic role of racE. LacZ fusion assays demonstrated that racE was expressed in both types of media but yrpC was expressed only in minimal medium, which accounted for the absence of yrpC function in rich medium. Neither racE nor yrpC was required for B. subtilis cells to synthesize poly-gamma-DL-glutamate (gamma-PGA),a capsule polypeptide Of D- and L-glutamate linked through a -gamma-carboxylamide bond. Wild-type cells degraded the capsule during the late stationary phase without accumulating the degradation products, D-glutamate and L-glutamate, in the medium. In contrast, racE or yrpC mutant cells accumulated significant amounts of D- but not L-glutamate. Exogenous D-glutamate utilization was somewhat defective in the mutants and the double mutation of racE and yrpC severely impaired D-amino acid utilization. Thus, both racemase genes appear necessary to complete the catabolism of exogenous D-glutamate generated from gamma-PGA.