Institut für Bio- und Geowissenschaften, IBG-1: Biotechnologie, Forschungszentrum Jülich, D-52425 Jülich, Germany.
J Biotechnol. 2012 Apr 30;158(4):231-41. doi: 10.1016/j.jbiotec.2011.06.003. Epub 2011 Jun 12.
Corynebacterium glutamicum possesses export systems for various amino acids including BrnFE, a two-component export system for L-methionine and the branched-chain amino acids L-valine, L-isoleucine and L-leucine. A gene for a putative transcriptional regulator of the Lrp family is transcribed divergently to the brnFE operon and is required for L-isoleucine export. By comparing global gene expression changes due to L-isoleucine addition we revealed increased brnFE expression in response to L-isoleucine in C. glutamicum wild type but not in an lrp deletion mutant. ChIP-to-chip analysis, band shift experiments and DNAse footprint analysis demonstrated that Lrp binds to the intergenic region between lrp and brnF. Expression analysis of transcriptional fusions with the lrp and brnFE promoters indicated that branched-chain amino acids and L-methionine when added to the growth medium stimulated brnFE expression in the order L-leucine > L-methionine > L-isoleucine > L-valine and that Lrp was required for activation of brnFE expression. Thus, regulation of brnFE by Lrp ensures that BrnFE is synthesized only if its substrate amino acids accumulate in cells which is commensurate with its role to counteract such situations of metabolic imbalance.
谷氨酸棒杆菌拥有多种氨基酸的输出系统，包括 BrnFE，这是一种用于 L-蛋氨酸和支链氨基酸 L-缬氨酸、L-异亮氨酸和 L-亮氨酸的双组分输出系统。一个 Lrp 家族假定转录调节因子的基因与 brnFE 操纵子转录方向相反，是 L-异亮氨酸输出所必需的。通过比较由于 L-异亮氨酸添加而导致的全局基因表达变化，我们发现在谷氨酸棒杆菌野生型中，L-异亮氨酸会引起 brnFE 表达增加，但在 lrp 缺失突变体中则不会。ChIP-chip 分析、带迁移实验和 DNAse 足迹分析表明，Lrp 结合在 lrp 和 brnF 之间的基因间区域。与 lrp 和 brnFE 启动子的转录融合表达分析表明，当支链氨基酸和 L-蛋氨酸添加到生长培养基中时，brnFE 的表达受到刺激，顺序为 L-亮氨酸> L-蛋氨酸> L-异亮氨酸> L-缬氨酸，并且 Lrp 是激活 brnFE 表达所必需的。因此，Lrp 对 brnFE 的调节确保只有在其底物氨基酸在细胞中积累时才合成 BrnFE，这与它抵消代谢失衡等情况的作用是一致的。
