Kinetic analysis by in vivo 31P nuclear magnetic resonance of internal Pi during the uptake of sn-glycerol-3-phosphate by the pho regulon-dependent Ugp system and the glp regulon-dependent GlpT system

Abstract

When sn-glycerol-3-phosphate (G3P) is taken up exclusively by the pho regulon-dependent Ugp transport system, it can be used as the sole source of P i but not as the sole source of carbon. We had previously suggested that the inability of G3P to be used as a carbon source under these conditions is due to trans inhibition of G3P uptake by internal P i derived from the degradation of G3P (P. Brzoska, M. Rimmele, K. Brzostek, and W. Boos, J. Bacteriol. 176:15-20, 1994). Here, we report 31 P nuclear magnetic resonance measurements of intact cells after exposure to G3P as well as to P i , using different mutants defective in pst (high-affinity P i transport), ugp (pho-dependent G3P transport), glpT (glp-dependent G3P transport), and glpD (aerobic G3P dehydrogenase). When G3P was transported by the Ugp system and when metabolism of G3P was allowed (glpD ؉ ), P i accumulated to about 13 to 19 mM. When G3P was taken up by the GlpT system, the preexisting internal P i pool (whether low or high) did not change. Both systems were inversly controlled by internal P i . Whereas the Ugp system was inhibited, the GlpT system was stimulated by elevated internal P i .sn-Glycerol-3-phosphate (G3P) can be taken up in Escherichia coli by several transport systems. When used as a carbon source, G3P is taken up exclusively by the GlpT transport system (1, 11, 13). This system is part of the glp regulon, a number of proteins whose genes are transcribed in response to the presence of glycerol and G3P in the medium and which are geared for the uptake and the metabolism of glycerol, G3P, and glycerol phosphoryl diesters (15). GlpT and all of the other glp-encoded proteins are under the control of GlpR, the repressor of the system (14), with G3P as the effective inducer (16). The GlpT transport system can function in two modes. In the exchange mode, G3P is taken up in exchange with internal P i (1,8). Uptake of G3P without P i exchange is essentially by proton symport. Under these conditions, GlpT-mediated uptake of G3P can serve as the sole source of P i . The GlpT permease is a tightly membrane-bound oligomeric complex of identical polypeptide subunits (13). G3P can also be taken up by the Ugp (uptake of glycerol phosphate) system. The Ugp system is a typical periplasmic binding protein-dependent multicomponent transport system specific for G3P and glyceryl phosphoryl phosphodiesters, the diacylation products of phospholipids (4, 21). The genes ugpB, ugpA, ugpE, ugpC, and ugpQ (18) form an operon located at 75 min on the E. coli chromosome encoding the specific binding protein (ugpB) (2), the two membrane-bound components (ugpA and ugpE), and the ATPbinding-fold-containing subunit (ugpC), which is supposedly the energy module of the system. The ugp operon is under the control of PhoB, the central gene activator of the pho regulon (3).The last transport system recognizing G3P is the Uhp system specific for hexose phosphates (12). Since Uhp is not induced in the absence of glucose-6-phosphate, it is not relevant to the phenomena discusse...

Proteomic Analyses of Intracellular Salmonella enterica Serovar Typhimurium Reveal Extensive Bacterial Adaptations to Infected Host Epithelial Cells

“…Interestingly, while the Ugp system was induced in response to phosphate limitation, the other G3P transporter, the Glp system, was significantly repressed at 6 h postinfection. This can be ascribed to some extent to the fact that GlpT is a G3P importer at the price of simultaneously being a phosphate exporter (63). In agreement with this notion, previous studies suggested that Glp-transported G3P can serve as the sole source for both carbon and phosphate, whereas Ugp-transported G3P can serve as the sole source only for phosphate (62,64).…”

Employment of a Promoter-Swapping Technique Shows that PhoU Modulates the Activity of the PstSCAB 2 ABC Transporter in Escherichia coli

“…This demonstrated that the cessation of growth of a ⌬phoU strain was not due to increased P i assimilation and sequestration and supported the suggestion that it may have been due to the accumulation of some inhibitory compound, which could have been intracellular P i or perhaps some phosphorylated metabolite (8,30). The intracellular levels of P i in E. coli range from 5 to 20 mM depending on the growth conditions and carbon source, and 10 mM is a common level during growth on glucose (24,29,34,35,40). Cells appear to possess a P i homeostasis mechanism that keeps the P i levels in this range (36).…”

The ABC maltose transporter

“…In addition to their essential function in transport, some ATPase subunits play an important role in the control of gene expression (see below). Furthermore, the glycerol phosphate (G3P) binding protein‐dependent transport system in E. coli is inhibited by internal inorganic phosphate (Pi) (Brzoska et al ., 1994; Xavier et al ., 1995). This inhibition cannot be observed when the ATP‐hydrolysing subunit UgpC is overexpressed.…”