Lee S J, Boos W, Bouché J P, Plumbridge J
Department of Biology, University of Konstanz, D-78457 Konstanz, Germany.
EMBO J. 2000 Oct 16;19(20):5353-61. doi: 10.1093/emboj/19.20.5353.
The global regulator Mlc controls several genes implicated in sugar utilization systems, notably the phosphotransferase system (PTS) genes, ptsG, manXYZ and ptsHI, as well as the malT activator. No specific low molecular weight inducer has been identified that can inactivate Mlc, but its activity appeared to be modulated by transport of glucose via Enzyme IICB(Glc) (PtsG). Here we demonstrate that inactivation of Mlc is achieved by sequestration of Mlc to membranes containing dephosphorylated Enzyme IICB(Glc). We show that Mlc binds specifically to membrane fractions which carry PtsG and that excess Mlc can inhibit Enzyme IICB(Glc) phosphorylation by the general PTS proteins and also Enzyme IICB(Glc)-mediated phosphorylation of alpha-methylglucoside. Binding of Mlc to Enzyme IICB(Glc) in vitro required the IIB domain and the IIC-B junction region. Moreover, we show that these same regions are sufficient for Mlc regulation in vivo, via cross-dephosphorylation of IIB(Glc) during transport of other PTS sugars. The control of Mlc activity by sequestration to a transport protein represents a novel form of signal transduction in gene regulation.
全局调控因子Mlc控制着几个与糖利用系统相关的基因，特别是磷酸转移酶系统（PTS）基因ptsG、manXYZ和ptsHI，以及malT激活因子。尚未鉴定出能使Mlc失活的特异性低分子量诱导物，但其活性似乎受葡萄糖通过酶IICB(Glc)（PtsG）转运的调节。在此，我们证明Mlc的失活是通过将Mlc隔离到含有去磷酸化酶IICB(Glc)的膜上来实现的。我们表明，Mlc特异性结合携带PtsG的膜组分，并且过量的Mlc可抑制一般PTS蛋白对酶IICB(Glc)的磷酸化作用，以及酶IICB(Glc)介导的α-甲基葡萄糖苷的磷酸化。Mlc在体外与酶IICB(Glc)的结合需要IIB结构域和IIC - B连接区域。此外，我们表明，在其他PTS糖的转运过程中，通过IIB(Glc)的交叉去磷酸化作用，这些相同区域在体内对于Mlc的调控也是足够的。通过隔离到转运蛋白来控制Mlc活性代表了基因调控中一种新型的信号转导形式。
