Inhibitory effect of acidic pH on OmpC porin: wild‐type and mutant studies

Liu, Nazhen; Delcour, Anne H.

doi:10.1016/s0014-5793(98)00975-2

Cited by 20 publications

(21 citation statements)

References 22 publications

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“…Finally, it is also important to consider whether the sensitivity of the mutant to acidic pH is due to the inability of this porin mutant to close at low pH. There have been numerous reports that acidic pH triggers closure of wild-type porins in electrophysiological experiments (25,35,42,43). We have confirmed this mode of porin regulation in vivo by comparing the flux of cephaloridine at pH 3.6 with that at pH 6.0 (in the absence of added polyamines).…”

Section: Resultssupporting

confidence: 61%

“…It is noteworthy that cells reduce their outer membrane permeability under acidic conditions by the use of multiple pathways that may act sequentially. The pH-induced closure of porins is immediate (25,35,42) and will rapidly lead to about a 20 to 25% reduction in permeability. This reduction is followed by the slower processes of regulation of gene expression, which affects the porin regulon and the cad operon.…”

Section: Resultsmentioning

confidence: 99%

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Cadaverine Inhibition of Porin Plays a Role in Cell Survival at Acidic pH

Samartzidou

Mehrazin

et al. 2003

J Bacteriol

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When grown at acidic pH, Escherichia coli cells secrete cadaverine, a polyamine known to inhibit porinmediated outer membrane permeability. In order to understand the physiological significance of cadaverine excretion and the inhibition of porins, we isolated an OmpC mutant that showed resistance to spermine during growth and polyamine-resistant porin-mediated fluxes. Here, we show that the addition of exogenous cadaverine allows wild-type cells to survive a 30-min exposure to pH 3.6 better than cells expressing the cadaverineinsensitive OmpC porin. Competition experiments between strains expressing either wild-type or mutant OmpC showed that the lack of sensitivity of the porin to cadaverine confers a survival disadvantage to the mutant cells at reduced pH. On the basis of these results, we propose that the inhibition of porins by excreted cadaverine represents a novel mechanism that provides bacterial cells with the ability to survive acid stress.

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Section: Resultssupporting

confidence: 61%

Section: Resultsmentioning

confidence: 99%

Cadaverine Inhibition of Porin Plays a Role in Cell Survival at Acidic pH

Samartzidou

Mehrazin

et al. 2003

J Bacteriol

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“…This may either indicate pH gating of the Rv1698 channel or a proton-induced conformational change of the constriction zone that causes a decreased conductivity for Tris-HCl. Both mechanisms were observed for porins of Gram-negative bacteria (33,34).…”

Section: Ion Selectivity Of the Rv1698mentioning

confidence: 90%

Rv1698 of Mycobacterium tuberculosis Represents a New Class of Channel-forming Outer Membrane Proteins

Siroy

Mailaender

Harder

et al. 2008

Journal of Biological Chemistry

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Mycobacteria contain an outer membrane composed of mycolic acids and a large variety of other lipids. Its protective function is an essential virulence factor of Mycobacterium tuberculosis. Only OmpA, which has numerous homologs in Gram-negative bacteria, is known to form channels in the outer membrane of M. tuberculosis so far. Rv1698 was predicted to be an outer membrane protein of unknown function. Expression of rv1698 restored the sensitivity to ampicillin and chloramphenicol of a Mycobacterium smegmatis mutant lacking the main porin MspA. Uptake experiments showed that Rv1698 partially complemented the permeability defect of the M. smegmatis porin mutant for glucose. These results indicated that Rv1698 provides an unspecific pore that can partially substitute for MspA. Lipid bilayer experiments demonstrated that purified Rv1698 is an integral membrane protein that indeed produces channels. The main single channel conductance is 4.5 ؎ 0.3 nanosiemens in 1 M KCl. Zero current potential measurements revealed a weak preference for cations. Whole cell digestion of recombinant M. smegmatis with proteinase K showed that Rv1698 is surface-accessible. Taken together, these experiments demonstrated that Rv1698 is a channel protein that is likely involved in transport processes across the outer membrane of M. tuberculosis. Rv1698 has single homologs of unknown functions in Corynebacterineae and thus represents the first member of a new class of channel proteins specific for mycolic acidcontaining outer membranes.Mycobacteria are classified as Gram-positive bacteria but have evolved a complex cell wall, comprising a peptidoglycanarabinogalactan polymer with covalently bound mycolic acids of considerable length (up to 90 carbon atoms) and a large variety of extractable lipids (1, 2). Most of these lipids are constituents of the cell envelope that provides an extraordinarily efficient permeability barrier and is an essential part of the intrinsic resistance of mycobacteria to many toxic compounds and antibiotics (3). To account for these observations, Minnikin (4) proposed a model in which the mycolic acids form the inner leaflet of an asymmetrical bilayer. Mutants and treatments affecting mycolic acid biosynthesis and the production of extractable lipids showed an increase in cell wall permeability and a drastic decrease in virulence, underlining the importance of the cell wall integrity for intracellular survival of Mycobacterium tuberculosis (1). Cryoelectron tomography revealed the native organization of the Mycobacterium smegmatis cell envelope. Further, the three-dimensional data and the investigation of ultrathin frozen-hydrated cryosections of M. smegmatis, M. bovis BCG, and Corynebacterium glutamicum identified the outermost layer as a lipid bilayer. Mycolic acids were shown to be essential components of this bilayer, therefore providing the first visualization of mycobacterial outer membranes in their native state (5).These findings raise the question of how the mycobacterial outer membrane is functionalized fo...

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“…17 Experiments performed on another E. coli porin OmpC revealed that acidic pH stabilizes the porin in a closed state without affecting the single channel conductance. 18 OmpG, a monomeric porin of E. coli also displayed pH induced modulation in acidic conditions, with an increased frequency of the single step transition between the open and the closed state. 19 The properties of TolC, a unique trimeric protein with an outer membrane b-barrel core and a a-helical periplasmic tunnel domain, 20 have also been investigated at various pH's, and acidic pH was found to cause a decrease in channel conductance.…”

Section: Introductionmentioning

confidence: 99%