Identification of Additional Players in the Alternative Biosynthesis Pathway to Isovaleryl-CoA in the Myxobacterium Myxococcus xanthus
Identification of Additional Players in the Alternative Biosynthesis Pathway to Isovaleryl-CoA in the Myxobacterium Myxococcus xanthus
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DOI：
10.1002/cbic.200800219
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发表时间：
2009-01-05
期刊：
影响因子：
3.2
通讯作者：
Mueller, Rolf
中科院分区：
文献类型：
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作者：
Bode, Helge B.;Ring, Michael W.;Mueller, Rolf
异戊酰辅酶A(IV-CoA)通常是通过BKD(支链酮酸脱氢酶)复合体降解亮氨酸而产生的。我们之前已经确定了粘杆菌中IV-CoA形成的另一条途径，该途径是众所周知的甲氧戊酸依赖的异戊二烯生物合成途径的分支。我们在黄色粘球菌中发现了3-羟基-3-甲基戊二酰辅酶A(HMG-CoA)合成酶(MVAS)参与了这一途径，该途径是在亮氨酸降解受损的突变体(如BKD(-))或在粘细菌子实体形成过程中诱导的。在这里，我们表明，亮氨酸降解所需的蛋白质也参与了通过反向反应的有效催化而替代的IV-CoA生物合成途径。此外，我们进行了全球基因表达实验，并将营养野生型细胞与BKD突变体进行了比较，发现了一个在BKD突变体中高度上调的五基因操纵子，该操纵子包含MVAS和其他直接参与替代途径的基因。基于我们的实验，我们对HMG-CoA形成IV-CoA所需的基因进行了角色分配。此外，在BKD突变体中，参与外膜生物合成的几个基因和大量编码调节蛋白的基因的表达水平降低，这解释了BKD突变体的复杂表型，包括在发育性深层培养中缺乏粘附性。
Isovaleryl-CoA (IV-CoA) is usually derived from the degradation of leucine by using the Bkd (branched-chain keto acid dehydrogenase) complex. We have previously identified an alternative pathway for IV-CoA formation in myxobacteria that branches from the well-known mevalonate-dependent isoprenoid biosynthesis pathway. We identified 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase (MvaS) to be involved in this pathway in Myxococcus xanthus, which is induced in mutants with impaired leucine degradation (e.g., bkd(-)) or during myxobacterial fruiting-body formation. Here, we show that the proteins required for leucine degradation are also involved in the alternative IV-CoA biosynthesis pathway through the efficient catalysis of the reverse reactions. Moreover, we conducted a global gene-expression experiment and compared vegetative wild-type cells with bkd mutants, and identified a five-gene operon that is highly up-regulated in bkd mutants and contains mvaS and other genes that ore directly involved in the alternative pathway. Based on our experiments, we assigned roles to the genes required for the formation of IV-CoA from HMG-CoA. Additionally, several genes involved in outer-membrane biosynthesis and a plethora of genes encoding regulatory proteins were decreased in expression levels in the bkd- mutant; this explains the complex phenotype of bkd mutants including a lack of adhesion in developmental submerse culture.