Tetramerization of the LexA Repressor in Solution: Implications for Gene Regulation of the E.coli SOS System at Acidic pH

Sousa, Francisco J.R.; Lima, Luis M.T.R.; Pacheco, Amílcar; Oliveira, C. L. P.; Torriani, Íris L.; Almeida, Darcy Fontoura de; Foguel, Débora; Silva, Jerson L.; Mohana‐Borges, Ronaldo

doi:10.1016/j.jmb.2006.03.069

Cited by 29 publications

(25 citation statements)

References 69 publications

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“…For example, equilibrium between Lac repressor dimers and tetramers modulates repression of lac operon expression [54,55]. E. coli LexA repressor dimer also forms higher aggregates, which affects its activity, and this is particularly important during adaptation to acid when lower pH turns on the SOS response independently of the RecA protein [56]. Presumably, this is part of a bacterial survival strategy for when the gastric acid barrier is crossed.…”

Section: Higher Lexa Oligomeric Formsmentioning

confidence: 99%

“…At pH 4.0, LexA repressor aggregates to tetramers and to larger oligomers, resulting in a drop in the concentration of dimers that can bind stably to DNA targets. At even lower pH (pH 2.5), a tetrameric state is adopted, and unfolding of the NTD DNA-binding domain causes a loss of specific DNA binding and an increase in nonspecific DNA binding [56]. At pH values close to the LexA isoelectric point (6.5) and at low salt concentration, the LexA repressor precipitates from concentrated solutions and cannot be redissolved.…”

Section: Higher Lexa Oligomeric Formsmentioning

confidence: 99%

“…Thus, when strains of E. coli pass into warm-blooded animals, they encounter many factors, for example acidic pH, that can induce the SOS response [56]. Another example is the production of antimicrobial molecules such as hydrogen peroxide by neutrophils that result in DNA damage and contribute to pathogenesis, for example in enterohemorrhagic E. coli [106].…”

Section: Variety In Sos Induction and The Lexa Regulonmentioning

confidence: 99%

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The bacterial LexA transcriptional repressor

Butala

Žgur-Bertok

Busby

2008

Cell. Mol. Life Sci.

268

244

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Bacteria respond to DNA damage by mounting a coordinated cellular response, governed by the RecA and LexA proteins. In Escherichia coli, RecA stimulates cleavage of the LexA repressor, inducing more than 40 genes that comprise the SOS global regulatory network. The SOS response is widespread among bacteria and exhibits considerable variation in its composition and regulation. In some well-characterised pathogens, induction of the SOS response modulates the evolution and dissemination of drug resistance, as well as synthesis, secretion and dissemination of the virulence. In this review, we discuss the structure of LexA protein, particularly with respect to distinct conformations that enable repression of SOS genes via specific DNA binding or repressor cleavage during the response to DNA damage. These may provide new starting points in the battle against the emergence of bacterial pathogens and the spread of drug resistance among them.

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Section: Higher Lexa Oligomeric Formsmentioning

confidence: 99%

Section: Higher Lexa Oligomeric Formsmentioning

confidence: 99%

Section: Variety In Sos Induction and The Lexa Regulonmentioning

confidence: 99%

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The bacterial LexA transcriptional repressor

Butala

Žgur-Bertok

Busby

2008

Cell. Mol. Life Sci.

268

244

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“…RecA-independent induction may relate to conformational changes of the repressor at low cytoplasmic pH. At low pH, the SOS response repressor (LexA) undergoes structural reorganization, causing LexA selfcleavage independent of RecA (32). Since the amino acid sequence of the C-terminal domain of the lambdoid repressor shares roughly 50% similarity with the sequence of LexA, a similar pattern of repressor tetramerization may account for the induction of expression of genes carried by Stx2-prophages in acid-stressed cells.…”

Section: Discussionmentioning

confidence: 99%

Induction of Shiga Toxin-Encoding Prophage by Abiotic Environmental Stress in Food

Fang

Mercer

McMullen

et al. 2017

Appl Environ Microbiol

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The prophage-encoded Shiga toxin is a major virulence factor in Stxproducing Escherichia coli (STEC). Toxin production and phage production are linked and occur after induction of the RecA-dependent SOS response. However, foodrelated stress and Stx-prophage induction have not been studied at the single-cell level. This study investigated the effects of abiotic environmental stress on stx expression by single-cell quantification of gene expression in STEC O104:H4 Δstx2::gfp:: amp r . In addition, the effect of stress on production of phage particles was determined. The lethality of stressors, including heat, HCl, lactic acid, hydrogen peroxide, and high hydrostatic pressure, was selected to reduce cell counts by 1 to 2 log CFU/ml. The integrity of the bacterial membrane after exposure to stress was measured by propidium iodide (PI). The fluorescent signals of green fluorescent protein (GFP) and PI were quantified by flow cytometry. The mechanism of prophage induction by stress was evaluated by relative gene expression of recA and cell morphology. Acid (pH Ͻ 3.5) and H 2 O 2 (2.5 mM) induced the expression of stx 2 in about 18% and 3% of the population, respectively. The mechanism of prophage induction by acid differs from that of induction by H 2 O 2 . H 2 O 2 induction but not acid induction corresponded to production of infectious phage particles, upregulation of recA, and cell filamentation. Pressure (200 MPa) or heat did not induce the Stx2-encoding prophage (Stx2-prophage). Overall, the quantification method developed in this study allowed investigation of prophage induction and physiological properties at the single-cell level. H 2 O 2 and acids mediate different pathways to induce Stx2-prophage.IMPORTANCE Induction of the Stx-prophage in STEC results in production of phage particles and Stx and thus relates to virulence as well as the transduction of virulence genes. This study developed a method for a detection of the induction of Stxprophages at the single-cell level; membrane permeability and an indication of SOS response to environmental stress were additionally assessed. H 2 O 2 and mitomycin C induced expression of the prophage and activated a SOS response. In contrast, HCl and lactic acid induced the Stx-prophage but not the SOS response. The lifestyle of STEC exposes the organism to intestinal and extraintestinal environments that impose oxidative and acid stress. A more thorough understanding of the influence of food processing-related stressors on Stx-prophage expression thus facilitates control of STEC in food systems by minimizing prophage induction during food production and storage.KEYWORDS single-cell detection, E. coli O104:H4, prophage induction, environmental stress, RecA-independent SOS response, membrane permeability, STEC, Shiga toxin, Shiga toxin-producing E. coli S higa toxin-producing Escherichia coli (STEC) causes the life-threatening hemolyticuremic syndrome (HUS), which is associated with acute renal failure and significant mortality (1, 2). Shiga toxins (Stx) include St...

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“…A stress sensitive phenotype was also reported for the recA mutant of Listeria monocytogenes EGD-e ( Figure 2) [16 ]. Interestingly, it has been shown for E. coli that a decrease in intracellular pH could result in structural changes of the LexA repressor protein, potentially resulting in RecA independent activation of the SOS response as well [23]. Another interesting observation was made for potential SOS response activation by salt in an in vitro system.…”

Section: Streptococcus Mutansmentioning

confidence: 99%