Counter-transport mediated by the lactose permease of Escherichia coli

Bentaboulet, Martine; Képès, Adam

doi:10.1016/0005-2736(77)90400-x

Cited by 22 publications

(13 citation statements)

References 15 publications

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“…Let us also note that, in another domain, the existence of these efflux permeases implies that all the past work on in vivo efflux of galactosides from the cell, performed prior to this important work, should be analysed retrospectively. Indeed the efflux of acetylated carbohydrates discovered accounts fairly well for the puzzling passive efflux of modified galactosides (alkylated thiogalactosides) when the two main energyyielding pathways are poisoned (28) : they would not be expelled from the cell by LacY, but by one or several of SetA, SetB or SetC. Do we have further arguments suggesting that there is indeed, under some circumstances, a steady-state or an overflow problem driven by the efficiency of LacY?…”

Section: Introductionmentioning

confidence: 79%

Cells need safety valves

Danchin

2009

BioEssays

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In Escherichia coli, the role of lacA, the third gene of the lactose operon, has remained an enigma. I suggest that its role is the consequence of the need for cells to have safety valves that protect them from the osmotic effect created by their permeases. Safety valves allow them to cope with the buildup of osmotic pressure under accidental transient conditions. Multidrug resistance (MDR) efflux, thus named because of our anthropocentrism, is ubiquitous. Yet, the formation of simple leaks would result in futile influx/efflux cycles. Versatile modification enzymes with low sensitivity solve the problem if the modified metabolite is the one exported by MDR permeases. This may account for the pervasive presence of acetyltransferases, such as LacA, associated to acetylmetabolite exporters. This scenario of constraints imposed by efficient influx of metabolites provides us with a model that should be followed when constructing synthetic cells.

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Section: Introductionmentioning

confidence: 79%

Cells need safety valves

Danchin

2009

BioEssays

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“…Figure 7C and F shows that the addition of KCN or CCCP resulted in almost instantaneous processing, and thus translocation of the N‐terminus of the ‘S107’ moiety to the periplasm. In Escherichia coli , the transport of lactose by lac permease requires the electrochemical potential (Bentaboulet and Kepes, 1977). Therefore, the breakdown of the electrochemical potential 30 s after the addition of CCCP was verified by inhibition of [ 14 C]‐lactose uptake into cells expressing the VIII–S107(K5) gene, the product of which is non‐functional (see Fig.…”

Section: Resultsmentioning

confidence: 99%

Molecular function of the dual‐start motif in the λ S holin

Graschopf¹,

Bläsi²

1999

Molecular Microbiology

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SummaryThe l S gene represents the prototype of holin genes with a dual-start motif, which leads to the synthesis of two polypeptides, S105 and S107. They differ at their N-terminus by only two amino acids, Met-1 and Lys-2, at the beginning of the longer product. Despite the minor difference, the two proteins have opposing functions in lysis, with protein S107 being an inhibitor and protein S105 being an effector of`hole formation' in the inner membrane. Here, we have studied the molecular mechanism underlying the`lysis clock' contributed by the dual-start motif. We have used protein fusions in which the secretory signal sequence of the M13 procoat protein VIII has been abutted to the Nterminal Met residues of S105 and S107 respectively. S-dependent`hole formation' required removal of the signal sequence in both fusion proteins, as both the VIII±S105 and the VIII±S107 fusion proteins were nonfunctional when leader peptidase cleavage was inhibited. These results strongly supported the hypothesis that functional assembly of S proteins requires translocation of their N-terminus to the periplasm. Using signal sequence cleavage as a measure of translocation, we observed that the translocation kinetics of the N-terminus of the S107 moiety was reduced about threefold when compared with the N-terminus of the S105 moiety. Moreover, depolarization of the membrane resulted in an immediate cleavage of the signal sequence and`hole formation' exerted by the S107 moiety of the VIII±S107 fusion protein. A model is presented in which S107 with a reversed topology of its N-terminus interacts with S105 and poisons`hole formation'. Upon depolarization of the membrane, translocation of the N-terminus of S107 to the periplasm results in the functional assembly of S proteins, i.e. hole formation'.

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“…Effect of p H on Lactose Counterflow. When intact E. coli (Wong & Wilson, 1970;Bentaboulet & Kepes, 1977), right-side-out membrane vesicles or proteoliposomes containing the lac carrier protein (Newman & Wilson, 1980;Newman et al, 1981;Foster et al, 1982) are loaded with appropriate transport substrates and subsequently diluted into media containing the same substrate in radioactive form, transient influx of radioactive substrate is observed. The phenomenon is called "entrance counterflow", and its efficiency, in kinetic terms, is due in part to the frequency with which the carrier returns from the outer to the inner surface of the membrane in the loaded vs. the unloaded form.…”

Section: Generation Of A$ During Carrier-mediated Lactose Effluxmentioning

confidence: 99%

Mechanism of lactose translocation in proteoliposomes reconstituted with lac carrier protein purified from Escherichia coli. I. Effect of pH and imposed membrane potential on efflux, exchange, and counterflow

Ml¹,

Viitanen²,

Dl³

et al. 1983

Biochemistry

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Proteoliposomes reconstituted with purified lac carrier by octyl glucoside dilution and freeze-thaw/sonication [Newman, M. Biochemistry, 21, 56341 are unilamellar, 50-150 nm in diameter, and impermeable to ions. By use of this preparation, carrier-mediated lactose efflux down a concentration gradient was used to probe the mechanism of P-galactoside translocation. The maximum rate of efflux is pH dependent, increasing

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Counter-transport mediated by the lactose permease of Escherichia coli

Cited by 22 publications

References 15 publications

Cells need safety valves

Cells need safety valves

Molecular function of the dual‐start motif in the λ S holin

Mechanism of lactose translocation in proteoliposomes reconstituted with lac carrier protein purified from Escherichia coli. I. Effect of pH and imposed membrane potential on efflux, exchange, and counterflow

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