Saier M H, Novotny M J, Comeau-Fuhrman D, Osumi T, Desai J D
J Bacteriol. 1983 Sep;155(3):1351-7. doi: 10.1128/jb.155.3.1351-1357.1983.
An Escherichia coli strain which overproduces the lactose permease was used to investigate the mechanism of allosteric regulation of this permease and those specific for melibiose, glycerol, and maltose by the phosphoenolpyruvate-sugar phosphotransferase system (PTS). Thio-beta-digalactoside, a high affinity substrate of the lactose permease, released the glycerol and maltose permeases from inhibition by methyl-alpha-d-glucoside. Resumption of glycerol uptake occurred immediately upon addition of the galactoside. The effect was not observed in a strain which lacked or contained normal levels of the lactose permease, but growth of wild-type E. coli in the presence of isopropyl-beta-thiogalactoside plus cyclic AMP resulted in enhanced synthesis of the lactose permease so that galactosides relieved inhibition of glycerol uptake. Thiodigalactoside also relieved the inhibition of glycerol uptake caused by the presence of other PTS substrates such as fructose, mannitol, glucose, 2-deoxyglucose, and 5-thioglucose. Inhibition of adenylate cyclase activity by methyl-alpha-glucoside was also relieved by thiodigalactoside in E. coli T52RT provided that the lactose permease protein was induced to high levels. Cooperative binding of sugar and enzyme III(Glc) to the melibiose permease in Salmonella typhimurium was demonstrated, but no cooperativity was noted with the glycerol and maltose permeases. These results are consistent with a mechanism of PTS-mediated regulation of the lactose and melibiose permeases involving a fixed number of allosteric regulatory proteins (enzyme III(Glc)) which may be titrated by the increased number of substrate-activated permease proteins. This work suggests that the cooperativity in the binding of sugar substrate and enzyme III(Glc) to the permease, demonstrated previously in in vitro experiments, has mechanistic significance in vivo. It substantiates the conclusion that PTS-mediated regulation of non-PTS permease activities involves direct allosteric interaction between the permeases and enzyme III(Glc), the postulated regulatory protein of the PTS.
一株过量产生乳糖通透酶的大肠杆菌菌株被用于研究该通透酶以及磷酸烯醇式丙酮酸 - 糖磷酸转移酶系统（PTS）特异性针对蜜二糖、甘油和麦芽糖的通透酶的变构调节机制。硫代 -β - 二半乳糖苷是乳糖通透酶的高亲和力底物，它能使甘油和麦芽糖通透酶从α - 甲基 -d - 葡萄糖苷的抑制作用中释放出来。加入半乳糖苷后，甘油摄取立即恢复。在缺乏乳糖通透酶或乳糖通透酶含量正常的菌株中未观察到这种效应，但野生型大肠杆菌在异丙基 -β - 硫代半乳糖苷加环腺苷酸存在的情况下生长，会导致乳糖通透酶的合成增强，从而使半乳糖苷解除对甘油摄取的抑制。硫代二半乳糖苷还能解除由其他PTS底物（如果糖、甘露醇、葡萄糖、2 - 脱氧葡萄糖和5 - 硫代葡萄糖）的存在所引起的对甘油摄取的抑制。在大肠杆菌T52RT中，如果乳糖通透酶蛋白被诱导到高水平，硫代二半乳糖苷也能解除α - 甲基葡萄糖苷对腺苷酸环化酶活性的抑制。已证明在鼠伤寒沙门氏菌中糖与酶III（Glc）对蜜二糖通透酶有协同结合作用，但甘油和麦芽糖通透酶未观察到协同性。这些结果与PTS介导的乳糖和蜜二糖通透酶调节机制一致，该机制涉及固定数量的变构调节蛋白（酶III（Glc）），其可能被底物激活的通透酶蛋白数量增加所滴定。这项工作表明，先前在体外实验中证明的糖底物与酶III（Glc）对通透酶结合的协同性在体内具有机制意义。它证实了PTS介导的非PTS通透酶活性调节涉及通透酶与酶III（Glc）（PTS假定的调节蛋白）之间直接变构相互作用的结论。
