Microcin E492 forms ion channels in phospholipid bilayer membranes

Lagos, Rosalba; Wilkens, Marcela; Vergara, Cecilia; Cecchi, Ximena; Monasterio, Octavio

doi:10.1016/0014-5793(93)80096-d

Cited by 64 publications

(70 citation statements)

References 13 publications

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“…Antibacterial activity of Mcc appeared to be restricted to the Enterobacteriaceae species, closely related to the producer strain that directly competes with Klebsiella to occupy a spatial niche in the ecosystem (5,7). Mcc has been shown to exert its toxic effect by forming ion channels on the cell membrane of target cells in a receptor-mediated fashion, which leads to a rapid depolarization and thus permeabilization of the cell membrane (6,8,9). Unlike other bacteriocins, toxic forms of Mcc are produced mainly in the exponential phase and comparatively less toxic in the stationary phase (5,10).…”

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confidence: 99%

Microcin Amyloid Fibrils A Are Reservoir of Toxic Oligomeric Species

Shahnawaz

Soto

2012

Journal of Biological Chemistry

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Microcin E492 (Mcc), a low molecular weight bacteriocin produced by Klebsiella pneumoniae RYC492, has been shown to exist in two forms: soluble forms that are believed to be toxic to the bacterial cell by forming pores and non-toxic fibrillar forms that share similar biochemical and biophysical properties with amyloids associated with several human diseases. Here we report that fibrils polymerized in vitro from soluble forms sequester toxic species that can be released upon changing environmental conditions such as pH, ionic strength, and upon dilution. Our results indicate that basic pH (>8.5), low NaCl concentrations (<50 mM), and dilution (>10-fold) destabilize Mcc fibrils into more soluble species that are found to be toxic to the target cells. Additionally, we also found a similar conversion of non-toxic fibrils into highly toxic oligomers using Mcc aggregates produced in vivo. Moreover, the soluble protein released from fibrils is able to rapidly polymerize into amyloid fibrils under fibril-forming conditions and to efficiently seed aggregation of monomeric Mcc. Our findings indicate that fibrillar forms of Mcc constitute a reservoir of toxic oligomeric species that is released into the medium upon changing the environmental conditions. These findings may have substantial implications to understand the dynamic process of interconversion between toxic and non-toxic aggregated species implicated in protein misfolding diseases.Bacteriocins are a group of polypeptide antibiotics excreted by different bacterial genera including Gram-negative and Gram-positive species (1-3). Once released, they restrain the growth of competing bacterial strains in a receptor-mediated manner employing several mechanisms. Mcc 2 is a low molecular weight (ϳ7.8 kDa) bacteriocin produced by Klebsiella pneumoniae RYC492 (4 -6). Antibacterial activity of Mcc appeared to be restricted to the Enterobacteriaceae species, closely related to the producer strain that directly competes with Klebsiella to occupy a spatial niche in the ecosystem (5, 7). Mcc has been shown to exert its toxic effect by forming ion channels on the cell membrane of target cells in a receptor-mediated fashion, which leads to a rapid depolarization and thus permeabilization of the cell membrane (6,8,9). Unlike other bacteriocins, toxic forms of Mcc are produced mainly in the exponential phase and comparatively less toxic in the stationary phase (5, 10). Surprisingly, neither apparent differences in the amounts of Mcc nor degradation or post-translational modifications have been shown to be responsible for the loss of activity (11). Some reports have described that these changes in Mcc toxicity may be due to the production of a microcin antagonist known as enterochelin in the stationary phase (12). More recently, the loss of Mcc toxicity in the stationary phase has been attributed to changes in the folding and polymerization of Mcc into aggregated structures similar to amyloid fibrils (13). Compelling in vitro and in vivo studies have shown that the changes on the Mcc...

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confidence: 99%

Microcin Amyloid Fibrils A Are Reservoir of Toxic Oligomeric Species

Shahnawaz

Soto

2012

Journal of Biological Chemistry

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“…In this respect, it is possible to observe ring-shaped preamyloid oligomers formed by MccE492 (12). These structures, reminiscent of pores, are probably the toxic structure of MccE492, which is associated with membrane depolarization by ion-conducting channels (2). This feature resembles the toxic structures that have been postulated for protein misfolding diseases, in which this type of oligomer would also act through a mechanism of pore formation (46).…”

Section: Discussionmentioning

confidence: 87%

“…icrocin E492 (MccE492) belongs to a family of low-molecular-weight channel-forming bacteriocins produced by Klebsiella pneumoniae RYC492 (1,2). The group of genes necessary for the production of active MccE492 has been cloned and expressed in Escherichia coli (3,4).…”

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confidence: 99%

Microcin E492 Amyloid Formation Is Retarded by Posttranslational Modification

Marcoleta

Marín

Mercado

et al. 2013

Journal of Bacteriology

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b Microcin E492, a channel-forming bacteriocin with the ability to form amyloid fibers, is exported as a mixture of two forms: unmodified (inactive) and posttranslationally modified at the C terminus with a salmochelin-like molecule, which is an essential modification for conferring antibacterial activity. During the stationary phase, the unmodified form accumulates because expression of the maturation genes mceIJ is turned off, and microcin E492 is rapidly inactivated. The aim of this work was to demonstrate that the increase in the proportion of unmodified microcin E492 augments the ability of this bacteriocin to form amyloid fibers, which in turn decreases antibacterial activity. To this end, strains with altered proportions of the two forms were constructed. The increase in the expression of the maturation genes augmented the antibacterial activity during all growth phases and delayed the loss of activity in the stationary phase, while the ability to form amyloid fibers was markedly reduced. Conversely, a higher expression of microcin E492 protein produced concomitant decreases in the levels of the modified form and in antibacterial activity and a substantial increase in the ability to form amyloid fibers. The same morphology for these fibers, including those formed by only the unmodified version, was observed. Moreover, seeds formed using exclusively the nonmodified form were remarkably more efficient in amyloid formation with a shorter lag phase, indicating that the nucleation process is probably improved. Unmodified microcin E492 incorporation into amyloid fibers was kinetically more efficient than the modified form, probably due to the existence of a conformation that favors this process.

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“…Although ManYZ inhibition by MceA and MceB has a measurable effect on mannose (Biéler et al, 2006;de Lorenzo and Pugsley, 1985). Since MccE492 can form cation-specific channels by itself in lipid bilayers (Lagos et al, 1993), the lethal complex may or may not contain ManYZ. Although we have not directly assessed the presence of MceB, similar experiments with a Lactococcus bacteriocin system demonstrate the association of the tagged immunity protein in the complex (Diep et al, 2007 transport, it may not prevent the occasional penetration of a single bacteriophage DNA molecule.…”

Section: Co-expression Of Mcea and Mceb Interferes With Mannose Metabmentioning

confidence: 99%

The polypeptide core of Microcin E492 stably associates with the mannose permease and interferes with mannose metabolism

Biéler¹,

Silva²,

Belin³

2010

Research in Microbiology

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Microcin E492 (MccE492) is an antibacterial protein whose activity on target cells requires ManYZ, the inner membrane component of the mannose permease. We show here that MceA, the polypeptide core of MccE492, stably associates with ManYZ both in the presence and in the absence of MceB, the MccE492 immunity protein. The two known physiological activities of the mannose permease were assayed in cells coexpressing MceA and MceB. Under these conditions, growth on mannose as the sole carbon source is prevented; this was not observed in cells expressing only MceB. In contrast, susceptibility to bacteriophage l infection was not affected.

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Microcin E492 forms ion channels in phospholipid bilayer membranes

Cited by 64 publications

References 13 publications

Microcin Amyloid Fibrils A Are Reservoir of Toxic Oligomeric Species

Microcin Amyloid Fibrils A Are Reservoir of Toxic Oligomeric Species

Microcin E492 Amyloid Formation Is Retarded by Posttranslational Modification

The polypeptide core of Microcin E492 stably associates with the mannose permease and interferes with mannose metabolism

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