Molecular aspects of phosphate transport in Escherichia coli

Abstract

Escherichia coli transports inorganic phosphate (Pi) by the low-affinity transport system, Pit. When the level of the external Pi is lower than 20 microM, another transport system, Pst, is induced with a Kt of 0.25 microM. An outer-membrane porin, PhoE, with a Km of about 1 microM is also induced. The outer membrane allows the intake of organic phosphates which are degraded to Pi by phosphatases in the periplasm. The Pi-binding protein will capture the free Pi produced in the periplasm and direct it to the transmembrane channel of the cytoplasmic membrane. The channel consists of two proteins, PstA and PstC, which have six and five transmembrane helices, respectively. On the cytoplasmic side of the membrane the channel is linked to the PstB protein, which carries a nucleotide (probably ATP)-binding site. PstB probably provides the energy required by the channel to free Pi. The Pst system has two functions in E. coli: (i) the transport of Pi, and (ii) the negative regulation of the phosphate regulon (a complex of 20 proteins mostly related to organic phosphate transport). It is remarkable that these two functions are not related, since the repressibility of the regulon depends on the integral structure of Pst (PiBP + PstA + PstC + PstB) and not on the Pi transported. Another gene of the pst operon, phoU, produces a protein involved in the negative regulation of the Pho regulon, but the mechanism of this function has not been explained. Thus the regulatory function of the Pst system remains obscure. Its basal level, present when Pi is abundant, is sufficient to repress the Pho regulon but the negative regulatory function is lost upon Pi starvation.

A Lycopersicon esculentum phosphate transporter (LePT1) involved in phosphorus uptake from a vesicular–arbuscular mycorrhizal fungus

“…Kinetic analysis has shown that Pi uptake occurs in a bi-phasic manner, and consists of high-affinity (K m 1-10 µM) and low-affinity (K m 100-1000 µM) uptake mechanisms in plants (Clarkson, 1984), bacteria (Rao & Torriani, 1990), yeast (Borst-Pauwels, 1981) and other fungi (Burns & Beever, 1977), including germ tubes of the mycorrhizal fungus, Gigaspora margarita (Thomson et al, 1990).…”

The high-affinity phosphate transporter Pst in Proteus mirabilis HI4320 and its importance in biofilm formation

“…The Pst system of P. mirabilis (Table 1), a multimeric, high-affinity inorganic phosphate (P i ) transporter, is induced at limiting extracellular P i concentrations (,1 mM, K app m of 0.2 mM) (Rao & Torriani, 1990;Rosenberg et al, 1977). pst mutants are highly attenuated in cochallenge colonization of the CBA mouse model (Burall et al, 2004;Jacobsen et al, 2008).…”

“…Crystal formation occurs due to the urease-catalysed hydrolysis of urea into ammonia, leading to an increase in the local pH and the precipitation of calcium, magnesium and phosphate ions (Morris et al, 1999). The pathogenesis of P. mirabilis UTIs is not at present understood fully.The Pst system of P. mirabilis (Table 1), a multimeric, high-affinity inorganic phosphate (P i ) transporter, is induced at limiting extracellular P i concentrations (,1 mM, K app m of 0.2 mM) (Rao & Torriani, 1990;Rosenberg et al, 1977). pst mutants are highly attenuated in cochallenge colonization of the CBA mouse model (Burall et al, 2004;Jacobsen et al, 2008).…”

Organophosphate Hydrolase Is a Lipoprotein and Interacts with Pi-specific Transport System to Facilitate Growth of Brevundimonas diminuta Using OP Insecticide as Source of Phosphate

“…Our work has clearly shown that OPH is a lipoprotein, and adds to a growing list of Tat-dependent lipoproteins in bacteria and archaea (20,44,47,48). Interestingly, OPH contains an alanine residue at the ϩ2 position and according to the sorting rules for E. coli lipoproteins (42) should be translocated to the outer The other components of the ABC-type phosphate acquisition system (PstA, PstB, and PstC) for which PstS is the periplasmic binding protein are also shown.…”

“…From the list of proteins, subunits of the F 1 F o -ATP synthase (␣, ␤, ␥), the phosphate ABC transporter substrate-binding protein (PstS) and efflux pump components AcrB and TolC were identified as candidate OPH interacting partners (Table 3). It is interesting to note that the identified peptides matched with proteins involved either in phosphate uptake (44) or in effluxing of xenobiotics (45), as organophosphates are xenobiotics that also contain a potential source of phosphate.…”