Molecular Basis for Bacterial Growth on Citrate or Malonate.
Molecular Basis for Bacterial Growth on Citrate or Malonate.
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DOI：
10.1128/ecosalplus.3.4.6
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发表时间：
2004-12-01
期刊：
影响因子：
--
通讯作者：
Dimroth, Peter
中科院分区：
文献类型：
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作者：
Dimroth, Peter
环境中的柠檬酸盐或丙二酸盐可被多种需氧或厌氧细菌降解。对于选定的例子，编码降解途径的特定酶的基因与编码的蛋白质及其催化机制一起描述。如果柠檬酸盐的特异性转运蛋白可用，则需氧细菌通过细胞的基本酶装置容易地降解柠檬酸盐。克雷伯氏肺炎菌中柠檬酸盐的厌氧降解需要所谓的底物活化模块，以利用柠檬酸盐裂解酶的磷酸核糖基脱磷酸辅酶A辅基将柠檬酸盐转化为其硫酯。随后将柠檬基硫酯裂解成草酰乙酸酯和乙酰基硫酯，随着周转的继续，由乙酰基硫酯形成新的柠檬基硫酯。丙二酸的降解同样包括具有磷酸核糖基脱磷酸辅酶A辅基的底物活化模块。在与辅基形成乙酰基硫酯后，机器准备翻转。然后乙酰基残基被丙二酰基残基交换，丙二酰基残基容易随着乙酰基硫酯的再生而脱羧。该设备足以在丙二酸盐上进行需氧生长，因为ATP是通过乙酸盐的氧化产生的。然而，柠檬酸盐或丙二酸盐的厌氧生长取决于所谓的能量守恒模块的额外酶。这允许脱羧能量转化成Na+离子的电化学梯度。柠檬酸发酵K.在肺炎杆菌中，Na+梯度由草酰乙酸脱羧酶形成，主要用于驱动柠檬酸盐主动转运到细胞中。将这种能量源用于此目的是可能的，因为ATP是通过底物磷酸化以众所周知的从丙酮酸到乙酸的顺序产生的。然而，在丙二酸发酵细菌红色丙二酸单胞菌中，没有底物水平磷酸化的反应可用，因此在丙二酸脱羧反应中形成的Na+梯度必须用作ATP合成的驱动力。
Environmental citrate or malonate is degraded by a variety of aerobic or anaerobic bacteria. For selected examples, the genes encoding the specific enzymes of the degradation pathway are described together with the encoded proteins and their catalytic mechanisms. Aerobic bacteria degrade citrate readily by the basic enzyme equipment of the cell if a specific transporter for citrate is available. Anaerobic degradation of citrate in Klebsiella pneumoniae requires the so-called substrate activation module to convert citrate into its thioester with the phosphoribosyl dephospho-CoA prosthetic group of citrate lyase. The citryl thioester is subsequently cleaved into oxaloacetate and the acetyl thioester, from which a new citryl thioester is formed as the turnover continues. The degradation of malonate likewise includes a substrate activation module with a phosphoribosyl dephospho-CoA prosthetic group. The machinery gets ready for turnover after forming the acetyl thioester with the prosthetic group. The acetyl residue is then exchanged by a malonyl residue, which is easily decarboxylated with the regeneration of the acetyl thioester. This equipment suffices for aerobic growth on malonate, since ATP is produced via the oxidation of acetate. Anaerobic growth on citrate or malonate, however, depends on additional enzymes of a so-called energy conservation module. This allows the conversion of decarboxylation energy into an electrochemical gradient of Na+ ions. In citrate-fermenting K. pneumoniae, the Na+ gradient is formed by the oxaloacetate decarboxylase and mainly used to drive the active transport of citrate into the cell. To use this energy source for this purpose is possible, since ATP is generated by substrate phosphorylation in the well-known sequence from pyruvate to acetate. In the malonate-fermenting bacterium Malonomonas rubra, however, no reactions for substrate level phosphorylation are available and the Na+ gradient formed in the malonate decarboxylation reaction must therefore be used as the driving force for ATP synthesis.