Escherichia coli abg genes enable uptake and cleavage of the folate catabolite p-aminobenzoyl-glutamate
Escherichia coli abg genes enable uptake and cleavage of the folate catabolite p-aminobenzoyl-glutamate
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DOI：
10.1128/jb.01940-06
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发表时间：
2007-05-01
影响因子：
3.2
通讯作者：
Green, Jacalyn M.
中科院分区：
文献类型：
--
作者：
Carter, Eric L.;Jager, Lindsey;Green, Jacalyn M.
大肠杆菌AbgT首先被鉴定为一种结构蛋白，能够在外源对氨基苯甲酰谷氨酸(M.J.Hussein，J.M.Green和B.P.Nichols，J.细菌素)上生长对氨基苯甲酸营养不良。180：6260-6268,1998)。ABG区包括abgA、abgB、abgT和OGT；这些基因可能受AbgR调控，AbgR是一种差异转录的LysR蛋白。用高拷贝数编码AbgT的野生型细胞对对氨基苯甲酰谷氨酸的摄取达到饱和(K-T=123muM)，而对照细胞对表达载体的摄取可以忽略不计。代谢毒物的添加抑制了对氨基苯甲酰谷氨酸的摄取，这与这一需要能量的过程是一致的。单独表达大量AbgT的细胞摄取的对氨基苯甲酰-谷氨酸不会迅速代谢成捕获在细胞内的形式，因为向这些细胞中添加非放射性的对氨基苯甲酰-谷氨酸会导致细胞内标记的快速丢失。加入非放射性对氨基苯甲酸酯不起作用。将abgA、abgB和abgAB基因克隆到中等拷贝数的表达载体pACYC184中，转化对氨基苯甲酸营养缺陷菌，发现对氨基苯甲酸营养缺陷菌在低水平的对氨基苯甲酰谷氨酸上生长能力增强。当用编码高拷贝水平的AbgT和中等拷贝水平的abgAB的互补质粒转化时，对氨基苯甲酸营养缺陷菌在50 nM的对氨基苯甲酰谷氨酸上生长。我们的数据与对氨基苯甲酰-谷氨酸的利用模型是一致的，在该模型中，AbgT催化对氨基苯甲酰-谷氨酸的转运，然后被由abgA和abgB编码的亚基组成的蛋白质裂解成对氨基苯甲酸。虽然在我们进行实验的条件下，这些基因的内源性表达非常低，但这些基因可能是由未知分子结合的AbgR诱导的。该区域真正的生理作用可能与某些类似于对氨基苯甲酰谷氨酸的分子有关，例如二肽。
Escherichia coli AbgT was first identified as a structural protein enabling the growth of p-aminobenzoate auxotrophs on exogenous p-aminobenzoyl-glutamate (M. J. Hussein, J. M. Green, and B. P. Nichols, J. Bacteriol. 180:6260-6268, 1998). The abg region includes abgA, abgB, abgT, and ogt; these genes may be regulated by AbgR, a divergently transcribed LysR-type protein. Wild-type cells transformed with a high-copy-number plasmid encoding abgT demonstrate saturable uptake of p-aminobenzoyl-glutamate (K-T = 123 mu M); control cells expressing vector demonstrate negligible uptake. The addition of metabolic poisons inhibited uptake of p-aminobenzoyl-glutamate, consistent with this process requiring energy. p-Aminobenzoyl-glutamate taken in by cells expressing large amounts of AbgT alone is not rapidly metabolized to a form that is trapped in the cell, as the addition of nonradioactive p-aminobenzoyl-glutamate to these cells results in a rapid loss of intracellular label. The addition of nonradioactive p-aminobenzoate has no effect. The abgA, abgB, and abgAB genes were cloned into the medium-copy-number plasmid pACYC184; p-aminobenzoate auxotrophs transformed with the clone encoding abgAB demonstrated enhanced ability to grow on low levels of p-aminobenzoyl-glutamate. When transformed with complementary plasmids encoding high-copy levels of abgT and medium-copy levels of abgAB, p-aminobenzoate auxotrophs grew on 50 nM p-aminobenzoyl-glutamate. Our data are consistent with a model of p-aminobenzoyl-glutamate utilization in which AbgT catalyzes transport of paminobenzoyl-glutamate, followed by cleavage to p-aminobenzoate by a protein composed of subunits encoded by abgA and abgB. While endogenous expression of these genes is very low under the conditions in which we performed our experiments, these genes may be induced by AbgR bound to an unknown molecule. The true physiological role of this region may be related to some molecule similar to p-aminobenzoyl-glutamate, such as a dipeptide.