Department of Molecular Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, California, USA.
Department of Microbiology and Immunology, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt.
Microb Physiol. 2020;30(1-6):36-49. doi: 10.1159/000510257. Epub 2020 Sep 30.
The prokaryotic phosphoenolpyruvate (PEP):sugar phosphotransferase system (PTS) concomitantly transports and phosphorylates its substrate sugars. In a recent publication, we provided evidence that protein-protein interactions of the fructose-specific integral membrane transporter (FruAB) with other PTS sugar group translocators regulate the activities of the latter systems in vivo and sometimes in vitro. In this communication, we examine the consequences of the overexpression of several different transport systems on the activities of selected PTS and non-PTS permeases. We report that high levels of these transport systems enhance the in vivo activities of several other systems in a fairly specific fashion. Thus, (1) overexpression of ptsG (glucose porter) selectively enhanced mannitol, N-acetylglucosamine, and 2-deoxyglucose (2DG) uptake rates; (2) overexpression of mtlA (mannitol porter) promoted methyl α-glucoside (αMG) and 2DG uptake; (3) manYZ (but not manY alone) (mannose porter) overexpression enhanced αMG uptake; (4) galP (galactose porter) overexpression enhanced mannitol and αMG uptake; and (5) ansP (asparagine porter) overexpression preferentially enhanced αMG and 2DG uptake, all presumably as a result of direct protein-protein interactions. Thus, it appears that high level production of several integral membrane permeases enhances sugar uptake rates, with the PtsG and ManXYZ systems being most consistently stimulated, but the MtlA and NagE systems being more selectively stimulated and to a lesser extent. Neither enhanced expression nor in vitro PEP-dependent phosphorylation activities of the target PTS systems were appreciably affected. The results are consistent with the suggestion that integral membrane transport proteins form an interacting network in vivo with physiological consequences, dependent on specific transporters and their concentrations in the membrane.
原核磷酸烯醇丙酮酸（PEP）：糖磷酸转移酶系统（PTS）同时运输和磷酸化其底物糖。在最近的一篇出版物中，我们提供了证据，证明果糖特异性完整膜转运蛋白（FruAB）与其他 PTS 糖组转运蛋白的蛋白-蛋白相互作用调节了这些系统在体内和体外的活性。在本通讯中，我们研究了几种不同运输系统的过表达对选定 PTS 和非 PTS 透性酶活性的影响。我们报告说，这些运输系统的高水平以相当特定的方式增强了几种其他系统的体内活性。因此，（1）ptsG（葡萄糖载体）的过表达选择性增强了甘露醇、N-乙酰葡萄糖胺和 2-脱氧葡萄糖（2DG）的摄取速率；（2）mtlA（甘露醇载体）的过表达促进了甲基α-葡萄糖苷（αMG）和 2DG 的摄取；（3）manYZ（而非单独的 manY）（甘露糖载体）的过表达增强了αMG 的摄取；（4）galP（半乳糖载体）的过表达增强了甘露醇和αMG 的摄取；（5）ansP（天冬酰胺载体）的过表达优先增强了αMG 和 2DG 的摄取，所有这些都可能是由于直接的蛋白-蛋白相互作用。因此，似乎几种完整膜透性酶的高水平产生增强了糖的摄取速率，其中 PtsG 和 ManXYZ 系统受到的刺激最一致，但 MtlA 和 NagE 系统受到的刺激更具选择性，程度较小。目标 PTS 系统的增强表达或体外 PEP 依赖性磷酸化活性均未受到明显影响。这些结果与这样的观点一致，即完整膜转运蛋白在体内形成一个相互作用的网络，具有生理后果，取决于特定的转运蛋白及其在膜中的浓度。
