Pleiotropic transcriptional repressor CodY senses the intracellular pool of branched-chain amino acids in Lactococcus lactis
Pleiotropic transcriptional repressor CodY senses the intracellular pool of branched-chain amino acids in Lactococcus lactis
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DOI：
10.1046/j.1365-2958.2001.02470.x
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发表时间：
2001-06-01
影响因子：
3.6
通讯作者：
Delorme, C
中科院分区：
文献类型：
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作者：
Guédon, E;Serror, P;Delorme, C
蛋白质水解是乳酸乳球菌在乳中生长过程中必需的氨基酸。对L.乳酸菌的蛋白水解系统包括细胞壁蛋白酶（PrtP）、寡肽转运系统（Opp）和至少四种胞内肽酶（PepO 1、PepN、PepC、PepDA 2），这些蛋白水解系统都受到富氮源的负调控。prtP、opp-pepO 1、pepN和pepC基因的转录受培养基中二肽的调节。使用opp-lacZ融合分离在寡肽转运系统的表达中用于氮控制的去阻遏的随机插入突变体。三分之一的突变体被定位在同一个位点。失活基因的产物与枯草芽孢杆菌的CodY（二肽通透酶操纵子（dpp）的多效性阻遏物）和包括氨基酸降解和感受态诱导在内的多个基因具有48%的同源性。通过分析opp-lux融合对添加具有不同氨基酸组成的67种二肽的响应来搜索控制CodY依赖性阻遏的信号。充分的相关性被发现之间的二肽含量支链氨基酸（支链氨基酸，异亮氨酸，亮氨酸或缬氨酸）和它们的能力，介导的抑制opp-pepO 1的表达。特异性调节二肽的抑制作用在L.乳酸菌突变体在其运输或降解成氨基酸方面受到影响，表明信号依赖于细胞中的BCAA库。最后，opp-pepO 1表达的抑制在不能降解支链氨基酸的突变体中更强，强调支链氨基酸作为CodY活性信号的中心作用。这种调控模式表明，在L.乳酸菌和可能的其他革兰氏阳性细菌，CodY是一种多效性阻遏物，其感测作为细胞中BCAA库的函数的营养供应。
Proteolysis is essential for supplying Lactococcus lactis with amino acids during growth in milk. Expression of the major components of the L. lactis proteolytic system, including the cell wall proteinase (PrtP), the oligopeptide transport system (Opp) and at least four intracellular peptidases (PepO1, PepN, PepC, PepDA2), was shown previously to be controlled negatively by a rich nitrogen source. The transcription of prtP, opp-pepO1, pepN and pepC genes is regulated by dipeptides in the medium. Random insertion mutants derepressed for nitrogen control in the expression of the oligopeptide transport system were isolated using an opp-lacZ fusion. A third of the mutants were targeted in the same locus. The product of the inactivated gene shared 48% identity with CodY from Bacillus subtilis, a pleiotropic repressor of the dipeptide permease operon (dpp) and several genes including genes involved in amino acid degradation and competence induction. The signal controlling CodY-dependent repression was searched for by analysing the response of the opp-lux fusion to the addition of 67 dipeptides with different amino acid compositions. Full correlation was found between the dipeptide content in branched-chain amino acids (BCAA; isoleucine, leucine or valine) and their ability to mediate the repression of opp-pepO1 expression. The repressive effect resulting from specific regulatory dipeptides was abolished in L. lactis mutants affected in terms of their transport or degradation into amino acids, showing that the signal was dependent on the BCAA pool in the cell. Lastly, the repression of opp-pepO1 expression was stronger in a mutant unable to degrade BCAAs, underlining the central role of BCAAs as a signal for CodY activity. This pattern of regulation suggests that, in L. lactis and possibly other Gram-positive bacteria, CodY is a pleiotropic repressor sensing nutritional supply as a function of the BCAA pool in the cell.