Department of Molecular Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, CA, United States of America.
Department of Microbiology and Immunology, Faculty of Pharmacy, Ain Shams University, Abbassia, Cairo, Egypt.
PLoS One. 2019 Nov 21;14(11):e0219332. doi: 10.1371/journal.pone.0219332. eCollection 2019.
The multicomponent phosphoenolpyruvate (PEP)-dependent sugar-transporting phosphotransferase system (PTS) in Escherichia coli takes up sugar substrates from the medium and concomitantly phosphorylates them, releasing sugar phosphates into the cytoplasm. We have recently provided evidence that many of the integral membrane PTS permeases interact with the fructose PTS (FruA/FruB) [1]. However, the biochemical and physiological significance of this finding was not known. We have carried out molecular genetic/biochemical/physiological studies that show that interactions of the fructose PTS often enhance, but sometimes inhibit the activities of other PTS transporters many fold, depending on the target PTS system under study. Thus, the glucose (Glc), mannose (Man), mannitol (Mtl) and N-acetylglucosamine (NAG) permeases exhibit enhanced in vivo sugar transport and sometimes in vitro PEP-dependent sugar phosphorylation activities while the galactitol (Gat) and trehalose (Tre) systems show inhibited activities. This is observed when the fructose system is induced to high levels and prevented when the fruA/fruB genes are deleted. Overexpression of the fruA and/or fruB genes in the absence of fructose induction during growth also enhances the rates of uptake of other hexoses. The β-galactosidase activities of man, mtl, and gat-lacZ transcriptional fusions and the sugar-specific transphosphorylation activities of these enzyme transporters were not affected either by frustose induction or by fruAB overexpression, showing that the rates of synthesis of the target PTS permeases were not altered. We thus suggest that specific protein-protein interactions within the cytoplasmic membrane regulate transport in vivo (and sometimes the PEP-dependent phosphorylation activities in vitro) of PTS permeases in a physiologically meaningful way that may help to provide a hierarchy of preferred PTS sugars. These observations appear to be applicable in principle to other types of transport systems as well.
大肠杆菌中的多组分磷酸烯醇丙酮酸（PEP）依赖性糖转运磷酸转移酶系统（PTS）从培养基中摄取糖底物，并同时将其磷酸化，将糖磷酸释放到细胞质中。我们最近提供的证据表明，许多整合膜 PTS 通透酶与果糖 PTS（FruA/FruB）相互作用[1]。然而，这一发现的生化和生理意义尚不清楚。我们进行了分子遗传/生化/生理研究，结果表明，果糖 PTS 的相互作用通常会增强，但有时会抑制其他 PTS 转运蛋白的活性，倍数取决于所研究的目标 PTS 系统。因此，葡萄糖（Glc）、甘露糖（Man）、甘露醇（Mtl）和 N-乙酰葡萄糖胺（NAG）通透酶表现出增强的体内糖转运，有时在体外 PEP 依赖性糖磷酸化活性，而半乳糖醇（Gat）和海藻糖（Tre）系统则表现出抑制活性。当果糖系统被诱导到高水平时，会观察到这种情况，而当 fruA/fruB 基因缺失时，会阻止这种情况发生。在生长过程中不诱导果糖而过度表达 fruA 和/或 fruB 基因也会增强其他己糖的摄取速率。甘露糖、mtl 和 gat-lacZ 转录融合的β-半乳糖苷酶活性以及这些酶转运蛋白的糖特异性转磷酸化活性既不受果糖诱导的影响，也不受 fruAB 过表达的影响，表明目标 PTS 通透酶的合成速率没有改变。因此，我们认为细胞质膜内的特定蛋白-蛋白相互作用以一种生理上有意义的方式调节 PTS 通透酶的体内运输（有时还调节体外的 PEP 依赖性磷酸化活性），这可能有助于提供 PTS 糖的优先层次结构。这些观察结果原则上似乎也适用于其他类型的运输系统。
