FtsL, an Essential Cytoplasmic Membrane Protein Involved in Cell Division in Escherichia coli

MraZ Transcriptionally Controls the Critical Level of FtsL Required for Focusing Z-Rings and Kickstarting Septation in Bacillus subtilis

The bacterial division and cell wall (dcw) cluster is a highly conserved region of the genome which encodes several essential cell division factors, including the central divisome protein FtsZ. Understanding the regulation of this region is key to our overall understanding of the division process. mraZ is found at the 5' end of the dcw cluster, and previous studies have described MraZ as a sequence-specific DNA binding protein. In this article, we investigate MraZ to elucidate its role in Bacillus subtilis. Through our investigation, we demonstrate that increased levels of MraZ result in lethal filamentation due to repression of its own operon (mraZ-mraW-ftsL-pbpB). We observed rescue of filamentation upon decoupling ftsL expression, but not other genes in the operon, from MraZ control. Our data suggest that regulation of the mra operon may be an alternative way for cells to quickly arrest cytokinesis, potentially during entry into the stationary phase and in the event of DNA replication arrest. Furthermore, through time-lapse microscopy, we were able to identify that overexpression of mraZ or depletion of FtsL results in decondensation of the FtsZ ring (Z-ring). Using fluorescent d-amino acid labeling, we also observed that coordinated peptidoglycan insertion at the division site is dysregulated in the absence of FtsL. Thus, we reveal that the precise role of FtsL is in Z-ring maturation and focusing septal peptidoglycan synthesis. IMPORTANCE MraZ is a highly conserved protein found in a diverse range of bacteria, including genome-reduced Mycoplasma. We investigated the role of MraZ in Bacillus subtilis and found that overproduction of MraZ is toxic due to cell division inhibition. Upon further analysis, we observed that MraZ is a repressor of its own operon, which includes genes that encode the essential cell division factors FtsL and PBP2B. We noted that decoupling of ftsL alone was sufficient to abolish MraZ-mediated cell division inhibition. Using time-lapse microscopy, we showed that under conditions where the FtsL level is depleted, the cell division machinery is unable to initiate cytokinesis. Thus, our results pinpoint that the precise role of FtsL is in concentrating septal cell wall synthesis to facilitate cell division.

The structural dynamics of full-length divisome transmembrane proteins FtsQ, FtsB, and FtsL in FtsQBL complex formation

FtsQBL is a transmembrane protein complex in the divisome of Escherichia coli that plays a critical role in regulating cell division. Although extensive efforts have been made to investigate the interactions between the three involved proteins, FtsQ, FtsB, and FtsL, the detailed interaction mechanism is still poorly understood. In this study, we used hydrogen-deuterium exchange mass spectrometry to investigate these full-length proteins and their complexes. We also dissected the structural dynamic changes and the related binding interfaces within the complexes. Our data revealed that FtsB and FtsL interact at both the periplasmic and transmembrane regions to form a stable complex. Furthermore, the periplasmic region of FtsB underwent significant conformational changes. With the help of computational modeling, our results suggest that FtsBL complexation may bring the respective constriction control domains (CCDs) in close proximity. We show that when FtsBL adopts a coiled-coil structure, the CCDs are fixed at a vertical position relative to the membrane surface; thus, this conformational change may be essential for FtsBL’s interaction with other divisome proteins. In the FtsQBL complex, intriguingly, we show only FtsB interacts with FtsQ at its C-terminal region, which stiffens a large area of the β-domain of FtsQ. Consistent with this, we found the connection between the α- and β-domains in FtsQ is also strengthened in the complex. Overall, the present study provides important experimental evidence detailing the local interactions between the full-length FtsB, FtsL, and FtsQ protein, as well as valuable insights into the roles of FtsQBL complexation in regulating divisome activity.

Lactococcus lactis Mutants Obtained From Laboratory Evolution Showed Elevated Vitamin K2 Content and Enhanced Resistance to Oxidative Stress

Vitamin K2 is an important vitamin for human health. Vitamin K2 enrichment in the human diet is possible by using vitamin K2-producing bacteria such as Lactococcus lactis in food fermentations. Based on previous observations that aerated cultivation conditions improved vitamin K2 content in L. lactis, we performed laboratory evolution on L. lactis MG1363 by cultivating this strain in a shake flask in a sequential propagation regime with transfers to a fresh medium every 72h. After 100 generations of propagation, we selected three evolved strains that showed improved stationary phase survival in oxygenated conditions. In comparison to the original strain MG1363, the evolved strains showed 50-110% increased vitamin K2 content and exhibited high resistance against hydrogen peroxide-induced oxidative stress. Genome sequencing of the evolved strains revealed common mutations in the genes ldh and gapB. Proteomics analysis revealed overproduction of glyceraldehyde 3-phosphate dehydrogenase (GapA), universal stress protein A2 (UspA2), and formamidopyrimidine-DNA glycosylase (MutM) under aerated conditions in evolved strains, proteins with putative functions in redox reactions, universal stress response, and DNA damage repair, all of which could contribute to the enhanced oxidative stress resistance. The mechanisms underlying elevated vitamin K2 content in the evolved strains remain to be elucidated. Two out of the three evolved strains performed similar to the original strain MG1363 in terms of growth and acidification of culture media. In conclusion, this study demonstrated a natural selection approach without genetic manipulations to obtain vitamin K2 overproducers that are highly relevant for food applications and contributed to the understanding of oxidative stress resistance in L. lactis.

A conserved subcomplex within the bacterial cytokinetic ring activates cell wall synthesis by the FtsW-FtsI synthase

Cell division in bacteria is mediated by a multiprotein assembly called the divisome. A major function of this machinery is the synthesis of the peptidoglycan (PG) cell wall that caps the daughter poles and prevents osmotic lysis of the newborn cells. Recent studies have implicated a complex of FtsW and FtsI (FtsWI) as the essential PG synthase within the divisome; however, how PG polymerization by this synthase is regulated and coordinated with other activities within the machinery is not well understood. Previous results have implicated a conserved subcomplex of division proteins composed of FtsQ, FtsL, and FtsB (FtsQLB) in the regulation of FtsWI, but whether these proteins act directly as positive or negative regulators of the synthase has been unclear. To address this question, we purified a five-member Pseudomonas aeruginosa division complex consisting of FtsQLB-FtsWI. The PG polymerase activity of this complex was found to be greatly stimulated relative to FtsWI alone. Purification of complexes lacking individual components indicated that FtsL and FtsB are sufficient for FtsW activation. Furthermore, support for this activity being important for the cellular function of FtsQLB was provided by the identification of two division-defective variants of FtsL that still form normal FtsQLB-FtsWI complexes but fail to activate PG synthesis. Thus, our results indicate that the conserved FtsQLB complex is a direct activator of PG polymerization by the FtsWI synthase and thereby define an essential regulatory step in the process of bacterial cell division.

Persistent Mycobacterium tuberculosis infection in mice requires PerM for successful cell division

The ability of Mycobacterium tuberculosis (Mtb) to persist in its host is central to the pathogenesis of tuberculosis, yet the underlying mechanisms remain incompletely defined. PerM, an integral membrane protein, is required for persistence of Mtb in mice. Here, we show that perM deletion caused a cell division defect specifically during the chronic phase of mouse infection, but did not affect Mtb’s cell replication during acute infection. We further demonstrate that PerM is required for cell division in chronically infected mice and in vitro under host-relevant stresses because it is part of the mycobacterial divisome and stabilizes the essential divisome protein FtsB. These data highlight the importance of sustained cell division for Mtb persistence, define condition-specific requirements for cell division and reveal that survival of Mtb during chronic infection depends on a persistence divisome.

Characterization of Conserved and Novel Septal Factors in Mycobacterium smegmatis

Septation in bacteria requires coordinated regulation of cell wall biosynthesis and hydrolysis enzymes so that new septal cross-wall can be appropriately constructed without compromising the integrity of the existing cell wall. Bacteria with different modes of growth and different types of cell wall require different regulators to mediate cell growth and division processes. Mycobacteria have both a cell wall structure and a mode of growth that are distinct from well-studied model organisms and use several different regulatory mechanisms. Here, using Mycobacterium smegmatis, we identify and characterize homologs of the conserved cell division regulators FtsL and FtsB, and show that they appear to function similarly to their homologs in Escherichia coli We identify a number of previously undescribed septally localized factors which could be involved in cell wall regulation. One of these, SepIVA, has a DivIVA domain, is required for mycobacterial septation, and is localized to the septum and the intracellular membrane domain. We propose that SepIVA is a regulator of cell wall precursor enzymes that contribute to construction of the septal cross-wall, similar to the putative elongation function of the other mycobacterial DivIVA homolog, Wag31.IMPORTANCE The enzymes that build bacterial cell walls are essential for cell survival but can cause cell lysis if misregulated; thus, their regulators are also essential. The number and nature of these regulators is likely to vary in bacteria that grow in different ways. The mycobacteria are a genus that have a cell wall whose composition and construction vary greatly from those of well-studied model organisms. In this work, we identify and characterize some of the proteins that regulate the mycobacterial cell wall. We find that some of these regulators appear to be functionally conserved with their structural homologs in evolutionarily distant species such as Escherichia coli, but other proteins have critical regulatory functions that may be unique to the actinomycetes.

YvqE and CovRS of Group A Streptococcus Play a Pivotal Role in Viability and Phenotypic Adaptations to Multiple Environmental Stresses

Streptococcus pyogenes (group A Streptococcus, or GAS) is a human pathogen that causes a wide range of diseases. For successful colonization within a variety of host niches, GAS utilizes TCSs to sense and respond to environmental changes and adapts its pathogenic traits accordingly; however, many GAS TCSs and their interactions remain uncharacterized. Here, we elucidated the roles of a poorly characterized TCS, YvqEC, and a well-studied TCS, CovRS, in 2 different GAS strain SSI-1 and JRS4, respectively. Deletion of yvqE and yvqC in JRS4 resulted in lower cell viability and abnormality of cell division when compared to the wild-type strain under standard culture conditions, demonstrating an important role for YvqEC. Furthermore, a double-deletion of yvqEC and covRS in SSI-1 and JRS4 resulted in a significantly impaired ability to survive under various stress conditions, as well as an increased sensitivity to cell wall-targeting antibiotics compared to that observed in either single mutant or wild-type strains suggesting synergistic interactions. Our findings provide new insights into the impact of poorly characterized TCS (YvqEC) and potential synergistic interactions between YvqEC and CovRS and reveal their potential role as novel therapeutic targets against GAS infection.

Bioinformatic Analyses of Unique (Orphan) Core Genes of the Genus Acidithiobacillus: Functional Inferences and Use As Molecular Probes for Genomic and Metagenomic/Transcriptomic Interrogation

Using phylogenomic and gene compositional analyses, five highly conserved gene families have been detected in the core genome of the phylogenetically coherent genus Acidithiobacillus of the class Acidithiobacillia. These core gene families are absent in the closest extant genus Thermithiobacillus tepidarius that subtends the Acidithiobacillus genus and roots the deepest in this class. The predicted proteins encoded by these core gene families are not detected by a BLAST search in the NCBI non-redundant database of more than 90 million proteins using a relaxed cut-off of 1.0e⁻⁵. None of the five families has a clear functional prediction. However, bioinformatic scrutiny, using pI prediction, motif/domain searches, cellular location predictions, genomic context analyses, and chromosome topology studies together with previously published transcriptomic and proteomic data, suggests that some may have functions associated with membrane remodeling during cell division perhaps in response to pH stress. Despite the high level of amino acid sequence conservation within each family, there is sufficient nucleotide variation of the respective genes to permit the use of the DNA sequences to distinguish different species of Acidithiobacillus, making them useful additions to the armamentarium of tools for phylogenetic analysis. Since the protein families are unique to the Acidithiobacillus genus, they can also be leveraged as probes to detect the genus in environmental metagenomes and metatranscriptomes, including industrial biomining operations, and acid mine drainage (AMD).

Impact of a Cross-Kingdom Signaling Molecule of Candida albicans on Acinetobacter baumannii Physiology

Multidrug-resistant (MDR) Acinetobacter baumannii is an opportunistic human pathogen that has become highly problematic in the clinical environment. Novel therapies are desperately required. To assist in identifying new therapeutic targets, the antagonistic interactions between A. baumannii and the most common human fungal pathogen, Candida albicans, were studied. We have observed that the C. albicans quorum-sensing molecule, farnesol, has cross-kingdom interactions, affecting the viability of A. baumannii. To gain an understanding of its mechanism, the transcriptional profile of A. baumannii exposed to farnesol was examined. Farnesol caused dysregulation of a large number of genes involved in cell membrane biogenesis, multidrug efflux pumps (AcrAB-like and AdeIJK-like), and A. baumannii virulence traits such as biofilm formation (csuA, csuB, and ompA) and motility (pilZ and pilH). We also observed a strong induction in genes involved in cell division (minD, minE, ftsK, ftsB, and ftsL). These transcriptional data were supported by functional assays showing that farnesol disrupts A. baumannii cell membrane integrity, alters cell morphology, and impairs virulence characteristics such as biofilm formation and twitching motility. Moreover, we showed that A. baumannii uses efflux pumps as a defense mechanism against this eukaryotic signaling molecule. Owing to its effects on membrane integrity, farnesol was tested to see if it potentiated the activity of the membrane-acting polymyxin antibiotic colistin. When coadministered, farnesol increased sensitivity to colistin for otherwise resistant strains. These data provide mechanistic understanding of the antagonistic interactions between diverse pathogens and may provide important insights into novel therapeutic strategies.

Identification and characterization of SlVKOR, a disulfide bond formation protein from Solanum lycopersicum, and bioinformatic analysis of plant VKORs

Homologs of vitamin K epoxide reductase (VKOR) exist widely in plants. However, only VKOR of Arabidopsis thaliana has been the subject of many studies to date. In the present study, the coding region of a VKOR from Solanum lycopersicum (JF951971 in GenBank) was cloned; it contained a membrane domain (VKOR domain) and an additional soluble thioredoxin-like (Trx-like) domain. Bioinformatic analysis showed that the first 47 amino acids in the N-terminus should act as a transit peptide targeting the protein to the chloroplast. Western blot demonstrated that the protein is localized in thylakoid membrane with the Trx-like domain facing the lumen. Modeling of three-dimensional structure showed that SlVKOR has a similar conformation with Arabidopsis and cyanobacterial VKORs, with five transmembrane segments in the VKOR domain and a typical Trx-like domain in the lumen. Functional assay showed that the full-length of SlVKOR with Trx-like domain without the transit peptide could catalyze the formation of disulfide bonds. Similar transit peptides at the N-terminus commonly exist in plant VKORs, most of them targeting to chloroplast according to prediction. Comparison of sequences and structures from different plants indicated that all plant VKORs possess two domains, a transmembrane VKOR domain and a soluble Trx-like domain, each having four conservative cysteines. The cysteines were predicted to be related to the function of catalyzing the formation of disulfide bonds.

Roles for both FtsA and the FtsBLQ subcomplex in FtsN-stimulated cell constriction in Escherichia coli

Escherichia coli FtsN is a bitopic membrane protein that is essential for triggering active cell constriction. A small periplasmic subdomain ((E) FtsN) is required and sufficient for function, but its mechanism of action is unclear. We isolated extragenic (E) FtsN*-suppressing mutations that restore division in cells producing otherwise non-functional variants of FtsN. These mapped to the IC domain of FtsA in the cytoplasm and to small subdomains of the FtsB and FtsL proteins in the periplasm. All FtsB and FtsL variants allowed survival without (E) FtsN, but many then imposed a new requirement for interaction between the cytoplasmic domain of FtsN ((N) FtsN) and FtsA. Alternatively, variants of FtsA, FtsB or FtsL acted synergistically to allow cell division in the complete absence of FtsN. Strikingly, moreover, substitution of a single residue in FtsB (E56) proved sufficient to rescue ΔftsN cells as well. In FtsN(+) cells, (E) FtsN*-suppressing mutations promoted cell fission at an abnormally small cell size, and caused cell shape and integrity defects under certain conditions. This and additional evidence support a model in which FtsN acts on either side of the membrane to induce a conformational switch in both FtsA and the FtsBLQ subcomplex to de-repress septal peptidoglycan synthesis and membrane invagination.

A role for the FtsQLB complex in cytokinetic ring activation revealed by an ftsL allele that accelerates division

The cytokinetic apparatus of bacteria is initially formed by the polymerization of the tubulin-like FtsZ protein into a ring structure at midcell. This so-called Z-ring facilitates the recruitment of many additional proteins to the division site to form the mature divisome machine. Although the assembly pathway leading to divisome formation has been well characterized, the mechanisms that trigger cell constriction remain unclear. In this report, we study a 'forgotten' allele of ftsL from Escherichia coli, which encodes a conserved division gene of unknown function. We discovered that this allele promotes the premature initiation of cell division. Further analysis also revealed that the mutant bypasses the requirement for the essential division proteins ZipA, FtsK and FtsN, and partially bypasses the need for FtsA. These findings suggest that rather than serving simply as a protein scaffold within the divisome, FtsL may play a more active role in the activation of the machine. Our results support a model in which FtsL, along with its partners FtsB and FtsQ, function as part of a sensing mechanism that promotes the onset of cell wall remodeling processes needed for the initiation of cell constriction once assembly of the divisome complex is deemed complete.

Site-directed fluorescence labeling reveals a revised N-terminal membrane topology and functional periplasmic residues in the Escherichia coli cell division protein FtsK

In Escherichia coli, FtsK is a large integral membrane protein that coordinates chromosome segregation and cell division. The N-terminal domain of FtsK (FtsKN) is essential for division, and the C terminus (FtsKC) is a well characterized DNA translocase. Although the function of FtsKN is unknown, it is suggested that FtsK acts as a checkpoint to ensure DNA is properly segregated before septation. This may occur through modulation of protein interactions between FtsKN and other division proteins in both the periplasm and cytoplasm; thus, a clear understanding of how FtsKN is positioned in the membrane is required to characterize these interactions. The membrane topology of FtsKN was initially determined using site-directed reporter fusions; however, questions regarding this topology persist. Here, we report a revised membrane topology generated by site-directed fluorescence labeling. The revised topology confirms the presence of four transmembrane segments and reveals a newly identified periplasmic loop between the third and fourth transmembrane domains. Within this loop, four residues were identified that, when mutated, resulted in the appearance of cellular voids. High resolution transmission electron microscopy of these voids showed asymmetric division of the cytoplasm in the absence of outer membrane invagination or visible cell wall ingrowth. This uncoupling reveals a novel role for FtsK in linking cell envelope septation events and yields further evidence for FtsK as a critical checkpoint of cell division. The revised topology of FtsKN also provides an important platform for future studies on essential interactions required for this process.

Cell division in Corynebacterineae

Bacterial cells must coordinate a number of events during the cell cycle. Spatio-temporal regulation of bacterial cytokinesis is indispensable for the production of viable, genetically identical offspring. In many rod-shaped bacteria, precise midcell assembly of the division machinery relies on inhibitory systems such as Min and Noc. In rod-shaped Actinobacteria, for example Corynebacterium glutamicum and Mycobacterium tuberculosis, the divisome assembles in the proximity of the midcell region, however more spatial flexibility is observed compared to Escherichia coli and Bacillus subtilis. Actinobacteria represent a group of bacteria that spatially regulate cytokinesis in the absence of recognizable Min and Noc homologs. The key cell division steps in E. coli and B. subtilis have been subject to intensive study and are well-understood. In comparison, only a minimal set of positive and negative regulators of cytokinesis are known in Actinobacteria. Nonetheless, the timing of cytokinesis and the placement of the division septum is coordinated with growth as well as initiation of chromosome replication and segregation. We summarize here the current knowledge on cytokinesis and division site selection in the Actinobacteria suborder Corynebacterineae.

RNase HIII from Chlamydophila pneumoniae can efficiently cleave double-stranded DNA carrying a chimeric ribonucleotide in the presence of manganese

Two ribonuclease Hs (RNase Hs) have been found in Chlamydophila pneumoniae, CpRNase HII and CpRNase HIII. This work is the first report that CpRNase HIII can efficiently cleave DNA-rN(1) -DNA/DNA (rN(1) , monoribonucleotide) in vitro in the presence of Mn(2+) , whereas the enzymatic activity of CpRNase HII on the same substrate was inhibited by Mn(2+) and dependent on Mg(2+) . However, the ability of both CpRNase Hs to cleave other alternative substrates (RNA/DNA hybrids and Okazaki-like substrates), was insensitive to the divalent ions changes, suggesting that high concentrations of Mn(2+) specifically repressed the ability of CpRNase HII to cleave DNA-rN(1) -DNA/DNA but activated this function in CpRNase HIII. Further in vivo experiments showed that the CpRNase HII complementation of Escherichia coli rnh(-) mutations in an Mg(2+) environment was suppressed by Mn(2+) . In contrast, Mn(2+) was indispensable for CpRNase HIII to complement the same mutations. Further, the cell growth inhibition and the genomic DNA sensitivity to alkali in the bacterial strain lacking RNase HII activity could be relieved by functional CpRNase HII or HIII with its compatible ion. Therefore, CpRNase HIII can execute cleavage activity on DNA-rN(1) -DNA/DNA under a Mn(2+) -rich environment and may function as a substitute for CpRNase HII under special physiological states.

Mutations at several loci cause increased expression of ribonucleotide reductase in Escherichia coli

Production of deoxyribonucleotides for DNA synthesis is an essential and tightly regulated process. The class Ia ribonucleotide reductase (RNR), the product of the nrdAB genes, is required for aerobic growth of Escherichia coli. In catalyzing the reduction of ribonucleotides, two of the cysteines of RNR become oxidized, forming a disulfide bond. To regenerate active RNR, the cell uses thioredoxins and glutaredoxins to reduce the disulfide bond. Strains that lack thioredoxins 1 and 2 and glutaredoxin 1 do not grow because RNR remains in its oxidized, inactive form. However, suppressor mutations that lead to RNR overproduction allow glutaredoxin 3 to reduce sufficient RNR for growth of these mutant strains. We previously described suppressor mutations in the dnaA and dnaN genes that had such effects. Here we report the isolation of new mutations that lead to increased levels of RNR. These include mutations that were not known to influence production of RNR previously, such as a mutation in the hda gene and insertions in the nrdAB promoter region of insertion elements IS1 and IS5. Bioinformatic analysis raises the possibility that IS element insertion in this region represents an adaptive mechanism in nrdAB regulation in E. coli and closely related species. We also characterize mutations altering different amino acids in DnaA and DnaN from those isolated before.

A protein oxidase catalysing disulfide bond formation is localized to the chloroplast thylakoids

In chloroplasts, thiol/disulfide-redox-regulated proteins have been linked to numerous metabolic pathways. However, the biochemical system for disulfide bond formation in chloroplasts remains undetermined. In the present study, we characterized an oxidoreductase, AtVKOR-DsbA, encoded by the gene At4g35760 as a potential disulfide bond oxidant in Arabidopsis. The gene product contains two distinct domains: an integral membrane domain homologous to the catalytic subunit of mammalian vitamin K epoxide reductase (VKOR) and a soluble DsbA-like domain. Transient expression of green fluorescent protein fusion in Arabidopsis protoplasts indicated that AtVKOR-DsbA is located in the chloroplast. The first 45 amino acids from the N-terminus were found to act as a transit peptide targeting the protein to the chloroplast. An immunoblot assay of chloroplast fractions revealed that AtVKOR-DsbA was localized in the thylakoid. A motility complementation assay showed that the full-length of AtVKOR-DsbA, if lacking its transit peptide, could catalyze the formation of disulfide bonds. Among the 10 cysteine residues present in the mature protein, eight cysteines (four in the AtVKOR domain and four in the AtDsbA domain) were found to be essential for promoting disulfide bond formation. The topological arrangement of AtVKOR-DsbA was assayed using alkaline phosphatase sandwich fusions. From these results, we developed a possible topology model of AtVKOR-DsbA in chloroplasts. We propose that the integral membrane domain of AtVKOR-DsbA contains four transmembrane helices, and that both termini and the cysteines involved in catalyzing the formation of disulfide bonds face the oxidative thylakoid lumen. These studies may help to resolve some of the issues surrounding the structure and function of AtVKOR-DsbA in Arabidopsis chloroplasts.

Identification of a novel function for the FtsL cell division protein from Escherichia coli K12

Analysis of the essential cell division protein FtsL demonstrates the partial conservation of a cysteine-pair within the trans-membrane region which itself is flanked by histidine-pairs in the cytosol and periplasm. Similar arrangements of such amino acids are seen in proteins known to transport/bind metal ions in biological systems. Heterologous expression of ftsL in Escherichia coli K12 confers a Zn(II)-sensitive phenotype and alteration of the candidate metal-ion binding residues cysteine or histidine substantially alters this phenotype. Whilst the cysteine/histidine replacement derivatives of ftsL were able to complement an otherwise ftsL-null strain, the derivative carrying ftsL lacking the cysteine pair was sensitive to raised metal-ion concentrations in the media. We show that ftsL can confer a metal-ion sensitive phenotype and that trans-membrane cysteine residues play a role in FtsL function in elevated metal-ion concentrations.

Identification of differentially expressed genes in three-pistil mutation in wheat using annealing control primer system

The common wheat line three-pistil (TP) is a valuable mutant for wheat breeding. The TP mutation has normal spike morphology; however, it only produces three pistils per floret. Therefore, it has potential to increase the grain number per spike. In order to determine the underlying molecular mechanism, an annealing control primer system was used to identify the different expressed genes in three-pistil mutation. Using 120 arbitrary ACP primers, we identified three differentially expressed genes in young spikes between two near-isogenic lines (i.e., Chuanmai 28 TP and Chinese Spring TP) and their recurrent parents. We tentatively designated the three differentially expressed genes as DETP-1, DETP-2, and DETP-3. DETP-1 showed similar function with maize cytoplasmic membrane protein, which is involved in cell division in bacteria. DETP-3 is homologous to maize endo-1, 4-beta-glucanase (EGases), which is associated with plant development, cell wall loosening, stem flowering, and root expansion. DETP-2 showed no significant hit with any sequence found in the database and translates unknown protein. These genes would likely play an important role in determining the three pistils trait in wheat.

Repurposing lipoic acid changes electron flow in two important metabolic pathways of Escherichia coli

In bacteria, cysteines of cytoplasmic proteins, including the essential enzyme ribonucleotide reductase (RNR), are maintained in the reduced state by the thioredoxin and glutathione/glutaredoxin pathways. An Escherichia coli mutant lacking both glutathione reductase and thioredoxin reductase cannot grow because RNR is disulfide bonded and nonfunctional. Here we report that suppressor mutations in the lpdA gene, which encodes the oxidative enzyme lipoamide dehydrogenase required for tricarboxylic acid (TCA) cycle functioning, restore growth to this redox-defective mutant. The suppressor mutations reduce LpdA activity, causing the accumulation of dihydrolipoamide, the reduced protein-bound form of lipoic acid. Dihydrolipoamide can then provide electrons for the reactivation of RNR through reduction of glutaredoxins. Dihydrolipoamide is oxidized in the process, restoring function to the TCA cycle. Thus, two electron transfer pathways are rewired to meet both oxidative and reductive needs of the cell: dihydrolipoamide functionally replaces glutathione, and the glutaredoxins replace LpdA. Both lipoic acid and glutaredoxins act in the reverse manner from their normal cellular functions. Bioinformatic analysis suggests that such activities may also function in other bacteria.

Membrane topology and mutational analysis of Mycobacterium tuberculosis VKOR, a protein involved in disulfide bond formation and a homologue of human vitamin K epoxide reductase

We have presented evidence that a homologue of vertebrate membrane protein vitamin K epoxide reductase (VKOR) is an important component of the protein disulfide bond-forming pathway in many bacteria. Bacterial VKOR appears to take the place of the nonhomologous DsbB found in Escherichia coli. We also determined the structure of a VKOR from a Cyanobacterium and showed that two or four conserved cysteines are required, according to different reductants for activity in an in vitro assay. Here we present evidence for the topologic arrangement in the cytoplasmic membrane of the VKOR from Mycobacterium tuberculosis (Mtb). The results show that Mtb VKOR is a membrane protein that spans the membrane 5 times with its N-terminus in the cytoplasm, C-terminus in the periplasm, and all four cysteines facing the periplasm. The essentiality of the four conserved cysteine residues has also been demonstrated in promoting disulfide bond formation in vivo and a mixed disulfide between a cysteine of DsbA of E. coli, and one of the cysteines (Cys(57)) of the VKOR homologue has been identified to be a likely intermediate in the disulfide bond-forming pathway. These studies may inform future resolution of issues surrounding the functioning of human VKOR.

Role of Escherichia coli FtsN protein in the assembly and stability of the cell division ring

Deprivation of FtsN, the last protein in the hierarchy of divisome assembly, causes the disassembly of other elements from the division ring, even extending to already assembled proto-ring proteins. Therefore the stability and function of the divisome to produce rings active in septation is not guaranteed until FtsN is recruited. Disassembly follows an inverse sequential pathway relative to assembly. In the absence of FtsN, the frequencies of FtsN and FtsQ rings are affected similarly. Among the proto-ring components, ZipA are more sensitive than FtsZ or FtsA rings. In contrast, removal of FtsZ leads to an almost simultaneous disappearance of the other elements from rings. Although restoration of FtsN allows for a quick reincorporation of ZipA into proto-rings, the de novo joint assembly of the three components when FtsZ levels are restored to FtsZ-deprived filaments is even faster. This suggests that the recruitment of ZipA into FtsZ-FtsA incomplete proto-rings may require first a period for the reversal of these partial assemblies.

Central domain of DivIB caps the C-terminal regions of the FtsL/DivIC coiled-coil rod

DivIB(FtsQ), FtsL, and DivIC(FtsB) are enigmatic membrane proteins that are central to the process of bacterial cell division. DivIB(FtsQ) is dispensable in specific conditions in some species, and appears to be absent in other bacterial species. The presence of FtsL and DivIC(FtsB) appears to be conserved despite very low sequence conservation. The three proteins form a complex at the division site, FtsL and DivIC(FtsB) being associated through their extracellular coiled-coil region. We report here structural investigations by NMR, small-angle neutron and x-ray scattering, and interaction studies by surface plasmon resonance, of the complex of DivIB, FtsL, and DivIC from Streptococcus pneumoniae, using soluble truncated forms of the proteins. We found that one side of the "bean"-shaped central beta-domain of DivIB interacts with the C-terminal regions of the dimer of FtsL and DivIC. This finding is corroborated by sequence comparisons across bacterial genomes. Indeed, DivIB is absent from species with shorter FtsL and DivIC proteins that have an extracellular domain consisting only of the coiled-coil segment without C-terminal conserved regions (Campylobacterales). We propose that the main role of the interaction of DivIB with FtsL and DivIC is to help the formation, or to stabilize, the coiled-coil of the latter proteins. The coiled-coil of FtsL and DivIC, itself or with transmembrane regions, could be free to interact with other partners.

Disulfide bond formation by exported glutaredoxin indicates glutathione's presence in the E. coli periplasm

Organisms have evolved elaborate systems that ensure the homeostasis of the thiol redox environment in their intracellular compartments. In Escherichia coli, the cytoplasm is kept under reducing conditions by the thioredoxins with the help of thioredoxin reductase and the glutaredoxins with the small molecule glutathione and glutathione reductase. As a result, disulfide bonds are constantly resolved in this compartment. In contrast to the cytoplasm, the periplasm of E. coli is maintained in an oxidized state by DsbA, which is recycled by DsbB. Thioredoxin 1, when exported to the periplasm turns from a disulfide bond reductase to an oxidase that, like DsbA, is dependent on DsbB. In this study we set out to investigate whether a subclass of the thioredoxin superfamily, the glutaredoxins, can become disulfide bond-formation catalysts when they are exported to the periplasm. We find that glutaredoxins can promote disulfide bond formation in the periplasm. However, contrary to the behavior of thioredoxin 1 in this environment, the glutaredoxins do so independently of DsbB. Furthermore, we show that glutaredoxin 3 requires the glutathione biosynthesis pathway for its function and can oxidize substrates with only a single active-site cysteine. Our data provides in vivo evidence suggesting that oxidized glutathione is present in the E. coli periplasm in biologically significant concentrations.

DjlA, a membrane-anchored DnaJ-like protein, is required for cytotoxicity of clam pathogen Vibrio tapetis to hemocytes

DjlA is an inner membrane cochaperone belonging to the DnaJ family, which has been shown to be involved in Legionella sp. pathogenesis. In this study, we explored the role of this protein in the physiology and virulence of Vibrio tapetis, the etiological agent of brown ring disease (BRD) in Manila clam (Ruditapes philippinarum). Analysis of the djlA locus in V. tapetis revealed a putative organization in an operon with a downstream gene that we designated duf924(Vt), which encodes a conserved protein with an unknown function and has homologues in bacteria and eukaryotes. djlA mutants displayed a reduced growth rate and showed an important loss of cytotoxic activity against R. philippinarum hemocytes in vitro, which could be restored by extrachromosomal expression of wild-type djlA(Vt) but not duf924(Vt). These results are in keeping with the potential importance of DjlA for bacterial pathogenicity and open new perspectives for understanding the mechanism of action of this protein in the novel V. tapetis-R. philippinarum interaction model.

Cell-division inhibitors: new insights for future antibiotics

The growing problem of antibiotic resistance has been exacerbated by the use of new drugs that are merely variants of older overused antibiotics. While it is naive to expect to restrain the spread of resistance without controlling antibacterial usage, the desperate need for drugs with novel targets has been recognized by health organizations, industry and academia alike. The wealth of knowledge available about the bacterial cell-division pathway has aided target-driven approaches to identify novel inhibitors. Here, we discuss the therapeutic potential of inhibiting bacterial cell division, and review the progress made in this exciting new area of antibacterial discovery.

In-frame deletion of Escherichia coli essential genes in complex regulon

A conditional knockout-rescue system was developed to construct an in-frame deletion strain ofEscherichia coli essential genes. The target was flanked with marker genes and FRT (FLP recognition target) sites, and a plasmid containing arabinose-induced FLP recombinase was transformed. After arabinose induction, cells could survive only when target protein activity was provided in trans. We selected three essential genes as targets, yaeT, fabZ, and dnaE, which are components of the complex eight-gene regulon yaeT-hlpA-lpxD-fabZ-lpxA-1pxB-rnhB-dnaE. Deletion of these three genes exhibit no polar effects on their adjacent genes in terms of cell viability, meaning that this system not only allows for the simplified study of protein interactions and homolog screening in other organisms, but also facilitates the null mutant construction of essential genes.

A eukaryotic-type serine/threonine protein kinase StkP of Streptococcus pneumoniae acts as a dimer in vivo

Streptococcus pneumoniae carries a single Ser/Thr protein kinase gene stkP in its genome. Biochemical studies performed with recombinant StkP have revealed that this protein is a functional membrane-linked eukaryotic-type Ser/Thr protein kinase. Here, we demonstrate that the deletion of its extracellular domain negatively affects the stability of a core kinase domain. In contrast, the membrane anchored kinase domain and the full-length form of StkP were stable and capable of autophosphorylation. Furthermore, evidence is presented that StkP forms dimers through its transmembrane and extracellular domains.

Premature targeting of cell division proteins to midcell reveals hierarchies of protein interactions involved in divisome assembly

In order to divide, the bacterium Escherichia coli must assemble a set of at least 10 essential proteins at the nascent division site. These proteins localize to midcell according to a linear hierarchy, suggesting that cell division proteins are added to the nascent divisome in strict sequence. We previously described a method, 'premature targeting', which allows us to target a protein directly to the division site independently of other cell division proteins normally required for its localization at midcell. By systematically applying this method to probe the recruitment of and associations among late cell division proteins, we show that this linear assembly model is likely incorrect. Rather, we find that the assembly of most of the late proteins can occur independently of 'upstream' proteins. Further, most late proteins, when prematurely targeted to midcell, can back-recruit upstream proteins in the reverse of the predicted pathway. Together these observations indicate that the late proteins, with the notable exception of the last protein in the pathway, FtsN, are associated in a hierarchical set of protein complexes. Based on these observations we present a revised model for assembly of the E. coli division apparatus.

In vivo requirement for glutaredoxins and thioredoxins in the reduction of the ribonucleotide reductases of Escherichia coli

Escherichia coli expresses three types of ribonucleotide reductases (RNRs) that utilize the redox chemistry of cysteine to catalyze the reduction of ribonucleotides. Upon reduction, the cysteines form a disulfide bond and must be reduced. The authors present in vivo studies that shed light on the mechanism by which these enzymes are regenerated. The class Ia enzyme, NrdAB, can be reduced by either the thioredoxins 1 and 2 or by glutaredoxin 1. The class Ib enzyme, NrdEF, is reduced in vivo by a dedicated glutaredoxin-like protein, NrdH. Despite its similarities to glutaredoxins, this protein is itself reduced by thioredoxin reductase in vivo. However, in the absence of thioredoxin reductase and NrdH, glutaredoxin 1 can partially replace NrdH. Despite their similar structures, the NrdEF and NrdAB RNRs differ in their abilities to function under low oxygen conditions. With only traces of oxygen present, NrdAB can allow some growth in the absence of the anaerobic enzyme NrdDG. NrdEF cannot. Furthermore, in anaerobiosis, E. coli is dependent for growth on class III RNR, NrdDG, and on having at least one of the two reductive systems, thioredoxin reductase or glutathione reductase. These findings indicate a role for these enzymes either for NrdDG reactivation or some other essential anaerobic process.

A novel regulatory mechanism couples deoxyribonucleotide synthesis and DNA replication in Escherichia coli

We present evidence for a complex regulatory interplay between the initiation of DNA replication and deoxyribonucleotide synthesis. In Escherichia coli, the ATP-bound DnaA protein initiates chromosomal replication. Upon loading of the beta-clamp subunit (DnaN) of the replicase, DnaA is inactivated as its intrinsic ATPase activity is stimulated by the protein Hda. The beta-subunit acts as a matchmaker between Hda and DnaA. Chain elongation of DNA requires a sufficient supply of deoxyribonucleotides (dNTPs), which are produced by ribonucleotide reductase (RNR). We present evidence suggesting that the molecular switch from ATP-DnaA to ADP-DnaA is a critical step coordinating DNA replication with increased deoxyribonucleotide synthesis. Characterization of dnaA and dnaN mutations that result in a constitutively high expression of RNR reveal this mechanism. We propose that the nucleotide bound state of DnaA regulates the transcription of the genes encoding ribonucleotide reductase (nrdAB). Accordingly, the conversion of ATP-DnaA to ADP-DnaA after initiation and loading of the beta-subunit DnaN would allow increased nrdAB expression, and consequently, coordinated RNR synthesis and DNA replication during the cell cycle.

Bacterial cell division: the mechanism and its precison

The recent development of cell biology techniques for bacteria to allow visualization of fundamental processes in time and space, and their use in synchronous populations of cells, has resulted in a dramatic increase in our understanding of cell division and its regulation in these tiny cells. The first stage of cell division is the formation of a Z ring, composed of a polymerized tubulin-like protein, FtsZ, at the division site precisely at midcell. Several membrane-associated division proteins are then recruited to this ring to form a complex, the divisome, which causes invagination of the cell envelope layers to form a division septum. The Z ring marks the future division site, and the timing of assembly and positioning of this structure are important in determining where and when division will take place in the cell. Z ring assembly is controlled by many factors including negative regulatory mechanisms such as Min and nucleoid occlusion that influence Z ring positioning and FtsZ accessory proteins that bind to FtsZ directly and modulate its polymerization behavior. The replication status of the cell also influences the positioning of the Z ring, which may allow the tight coordination between DNA replication and cell division required to produce two identical newborn cells.

An increased level of alternative sigma factor RpoS partially suppresses drug hypersensitivity associated with inactivation of the multidrug resistance pump AcrAB in Escherichia coli

Constitutive expression of stationary phase alternative sigma factor RpoS in Escherichia coli during the exponential phase was found to partially suppress drug sensitivity associated with an acrAB mutation that inactivates the major multidrug resistance pump, suggesting that Rpos might significantly contribute to multidrug resistance, underscoring yet another role for this important stress-related transcription factor.

In vitro reconstitution of a trimeric complex of DivIB, DivIC and FtsL, and their transient co-localization at the division site in Streptococcus pneumoniae

DivIB, DivIC and FtsL are bacterial proteins essential for cell division, which show interdependencies for their stabilities and localization. We have reconstituted in vitro a trimeric complex consisting of the recombinant extracellular domains of the three proteins from Streptococcus pneumoniae. The extracellular domain of DivIB was found to associate with a heterodimer of those of DivIC and FtsL. The heterodimerization of DivIC and FtsL was artificially constrained by fusion with interacting coiled-coils. Immunofluorescence experiments showed that DivIC is always localized at mid-cell, in contrast to DivIB and FtsL, which are co-localized with DivIC only during septation. Taken together, our data suggest that assembly of the trimeric complex DivIB/DivIC/FtsL is regulated during the cell cycle through controlled formation of the DivIC/FtsL heterodimer.

A complex of the Escherichia coli cell division proteins FtsL, FtsB and FtsQ forms independently of its localization to the septal region

Three membrane proteins required for cell division in Escherichia coli, FtsQ, FtsL and FtsB, localize to the cell septum. FtsL and FtsB, which each contain a leucine zipper-like sequence, are dependent on each other for this localization, and each of them is dependent on FtsQ. However, FtsQ is found at the cell division site in the absence of FtsL and FtsB. FtsQ, in turn, requires FtsK for its localization. Here, we show that FtsL, FtsB and FtsQ form a complex in vivo. Strikingly, this complex forms in the absence of FtsK, which is required for the localization of all three proteins to the mid-cell. These findings indicate that the FtsL, FtsB, FtsQ interactions can take place in cells before movement to the mid-cell and that migration to this position might occur only after the formation of the complex. Evidence indicating the regions of the three proteins involved in complex formation is presented. These findings provide the first example of preassembly of a subcomplex of cell division proteins before their localization to the septal region.

Interactions of glutaredoxins, ribonucleotide reductase, and components of the DNA replication system of Escherichia coli

A strain of Escherichia coli missing three members of the thioredoxin superfamily, thioredoxins 1 and 2 and glutaredoxin 1, is unable to grow, a phenotype presumed to be due to the inability of cells to reduce the essential enzyme ribonucleotide reductase. Two classes of mutations can restore growth to such a strain. First, we have isolated a collection of mutations in the gene for the protein glutaredoxin 3 that suppress the growth defect. Remarkably, all eight independent mutations alter the same amino acid, methionine-43, changing it to valine, isoleucine, or leucine. From the position of the amino acid changes and their effects, we propose that these alterations change the protein so that its properties are closer to those of glutaredoxin 1. The second means of suppressing the growth defects of the multiply mutant strain was by mutations in the DNA replication genes, dnaA and dnaN. These mutations substantially increase the expression of ribonucleotide reductase, most likely by altering the interaction of the regulatory protein DnaA with the ribonucleotide reductase promoter. Our results suggest that this increase in the concentration of ribonucleotide reductase in the cell allows more effective interaction with glutaredoxin 3, thus restoring an effective pool of deoxyribonucleotides. Our studies present direct evidence that ribonucleotide reductase is the only essential enzyme that requires the three reductive proteins missing in our strains. Our results also suggest an unexpected regulatory interaction between the DnaA and DnaN proteins.

Bacterial shape

In free-living eubacteria an external shell of peptidoglycan opposes internal hydrostatic pressure and prevents membrane rupture and death. At the same time, this wall imposes on each cell a shape. Because shape is both stable and heritable, as is the ability of many organisms to execute defined morphological transformations, cells must actively choose from among a large repertoire of available shapes. How they do so has been debated for decades, but recently experiment has begun to catch up with theory. Two discoveries are particularly informative. First, specific protein assemblies, nucleated by FtsZ, MreB or Mbl, appear to act as internal scaffolds that influence cell shape, perhaps by correctly localizing synthetic enzymes. Second, defects in cell shape are correlated with the presence of inappropriately placed, metabolically inert patches of peptidoglycan. When combined with what we know about mutants affecting cellular morphology, these observations suggest that bacteria may fabricate specific shapes by directing the synthesis of two kinds of cell wall: a long-lived, rigid framework that defines overall topology, and a metabolically plastic peptidoglycan whose shape is directed by internal scaffolds.

Cytokinesis in bacteria

Work on two diverse rod-shaped bacteria, Escherichia coli and Bacillus subtilis, has defined a set of about 10 conserved proteins that are important for cell division in a wide range of eubacteria. These proteins are directed to the division site by the combination of two negative regulatory systems. Nucleoid occlusion is a poorly understood mechanism whereby the nucleoid prevents division in the cylindrical part of the cell, until chromosome segregation has occurred near midcell. The Min proteins prevent division in the nucleoid-free spaces near the cell poles in a manner that is beginning to be understood in cytological and biochemical terms. The hierarchy whereby the essential division proteins assemble at the midcell division site has been worked out for both E. coli and B. subtilis. They can be divided into essentially three classes depending on their position in the hierarchy and, to a certain extent, their subcellular localization. FtsZ is a cytosolic tubulin-like protein that polymerizes into an oligomeric structure that forms the initial ring at midcell. FtsA is another cytosolic protein that is related to actin, but its precise function is unclear. The cytoplasmic proteins are linked to the membrane by putative membrane anchor proteins, such as ZipA of E. coli and possibly EzrA of B. subtilis, which have a single membrane span but a cytoplasmic C-terminal domain. The remaining proteins are either integral membrane proteins or transmembrane proteins with their major domains outside the cell. The functions of most of these proteins are unclear with the exception of at least one penicillin-binding protein, which catalyzes a key step in cell wall synthesis in the division septum.

Penicillin-binding protein PBP2 of Escherichia coli localizes preferentially in the lateral wall and at mid-cell in comparison with the old cell pole

The localization of penicillin-binding protein 2 (PBP2) in Escherichia coli has been studied using a functional green fluorescent protein (GFP)-PBP2 fusion protein. PBP2 localized in the bacterial envelope in a spot-like pattern and also at mid-cell during cell division. PBP2 disappeared from mid-cell just before separation of the two daughter cells. It localized with a preference for the cylindrical part of the bacterium in comparison with the old cell poles, which are known to be inert with respect to peptidoglycan synthesis. In contrast to subunits of the divisome, PBP2 failed to localize at mid-cell when PBP3 was inhibited by the specific antibiotic aztreonam. Therefore, despite its dependency on active PBP3 for localization at mid-cell, it seems not to be an integral part of the divisome. Cells grown for approximately half a mass doubling time in the presence of the PBP2 inhibitor mecillinam synthesized nascent cell poles with an increased diameter, indicating that PBP2 is required for the maintenance of the correct diameter of the new cell pole.

YgbQ, a cell division protein in Escherichia coli and Vibrio cholerae, localizes in codependent fashion with FtsL to the division site

YgbQ is a cell division protein in Escherichia coli and Vibrio cholerae. In E. coli the ygbQ gene was discovered as a result of a computer search of the E. coli genome designed to find potential interacting partners for cell division protein FtsL. In V. cholerae, ygbQ was identified as an essential gene by using a transposon that fuses genes to an arabinose promoter. The role of YgbQ in cell division is supported by the following. Cells depleted of YgbQ in both organisms form long filaments, but DNA segregation is not affected. YgbQ localizes to the constriction site in wild-type E. coli cells. Localization of E. coli YgbQ to the constriction site depends on cell division proteins FtsQ and FtsL but not FtsW and FtsI, placing YgbQ in the sequential dependency order of proteins localizing to the division site. Localization of green fluorescent protein-FtsL also depends on YgbQ, indicating that FtsL and YgbQ colocalize to the division site in E. coli. Our results show colocalization of proteins to the bacterial midcell in E. coli and raise the possibility that these proteins interact in a coiled-coil structure.

An in vitro transposon system for highly regulated gene expression: construction of Escherichia coli strains with arabinose-dependent growth at low temperatures

Placing a gene of interest under the control of an inducible promoter greatly aids the purification, localization and functional analysis of proteins but usually requires the sub-cloning of the gene of interest into an appropriate expression vector. Here, we describe an alternative approach employing in vitro transposition of Tn Omega P(BAD) to place the highly regulable, arabinose inducible P(BAD) promoter upstream of the gene to be expressed. The method is rapid, simple and facilitates the optimization of expression by producing constructs with variable distances between the P(BAD) promoter and the gene. To illustrate the use of this approach, we describe the construction of a strain of Escherichia coli in which growth at low temperatures on solid media is dependent on threshold levels of arabinose. Other uses of the transposable promoter are also discussed.

Genetic selection for and molecular dynamic modeling of a protein transmembrane domain multimerization motif from a random Escherichia coli genomic library

In order to identify new transmembrane helix packing motifs in naturally occurring proteins, we have selected transmembrane domains from a library of random Escherichia coli genomic DNA fragments and screened them for homomultimerization via their abilities to dimerize the bacteriophage lambda cI repressor DNA-binding domain. Sequences were isolated using a modified lambda cI headpiece dimerization assay system, which was shown previously to measure transmembrane helix-helix association in the E. coli inner membrane. Screening resulted in the identification of several novel sequences that appear to mediate helix-helix interactions. One sequence, representing the predicted sixth transmembrane domain (TM6) of the E. coli protein YjiO, was chosen for further analysis. Using site-directed mutagenesis and molecular dynamics, a small set of models for YjiO TM6 multimerization interface interactions were generated. This work demonstrates the utility of combining in vivo genetic tools with computational systems for understanding membrane protein structure and assembly.

Vacuolating cytotoxin of Helicobacter pylori induces apoptosis in the human gastric epithelial cell line AGS

Helicobacter pylori induces cell death by apoptosis. However, the apoptosis-inducing factor is still unknown. The virulence factor vacuolating cytotoxin A (VacA) is a potential candidate, and thus its role in apoptosis induction was investigated in the human gastric epithelial cell line AGS. The supernatant from the vacA wild-type strain P12 was able to induce apoptotic cell death, whereas the supernatant from its isogenic mutant strain P14 could not. That VacA was indeed the apoptosis-inducing factor was demonstrated further by substantial reduction of apoptosis upon treatment of AGS cells with a supernatant specifically depleted of native VacA. Furthermore, a recombinant VacA produced in Escherichia coli was also able to induce apoptosis in AGS cells but failed to induce cellular vacuolation. These findings demonstrate that the vacuolating cytototoxin of H. pylori is a bacterial factor capable of inducing apoptosis in gastric epithelial cells.

Structures of ribonuclease P RNAs of Vibrio core species

The structures of an RNA component of ribonuclease P (RNase P RNA) were examined for Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio carchariae, Vibrio natriegens, Vibrio campbellii, Vibrio proteolyticus, Vibrio pelagius and Vibrio harveyi to clearly determine their genetic differences. The RNase P RNAs ranged from 382 to 454 nucleotides (nt) in size, and were remarkably different from each other in the structure of two helices, P3 and P12. The P3 helices were comprised of tandem repeats of a palindromic sequence (24 nt), resulting in the longitudinal repetition of a stem structure. The number of repetitions ranged from four in V. harveyi, to one in both V. alginolyticus and V. proteolyticus. The genes for the RNase P RNAs of all species were located between two open reading frames, the amino acid sequences of which were similar to the hypothetical proteins located at 70.92 and 1.94 min in the Escherichia coli chromosome.

Analysis of the essential cell division gene ftsL of Bacillus subtilis by mutagenesis and heterologous complementation

The ftsL gene is required for the initiation of cell division in a broad range of bacteria. Bacillus subtilis ftsL encodes a 13-kDa protein with a membrane-spanning domain near its N terminus. The external C-terminal domain has features of an alpha-helical leucine zipper, which is likely to be involved in the heterodimerization with another division protein, DivIC. To determine what residues are important for FtsL function, we used both random and site-directed mutagenesis. Unexpectedly, all chemically induced mutations fell into two clear classes, those either weakening the ribosome-binding site or producing a stop codon. It appears that the random mutagenesis was efficient, so many missense mutations must have been generated but with no phenotypic effect. Substitutions affecting hydrophobic residues in the putative coiled-coil domain, introduced by site-directed mutagenesis, also gave no observable phenotype except for insertion of a helix-breaking proline residue, which destroyed FtsL function. ftsL homologues cloned from three diverse Bacillus species, Bacillus licheniformis, Bacillus badius, and Bacillus circulans, could complement an ftsL null mutation in B. subtilis, even though up to 66% of the amino acid residues of the predicted proteins were different from B. subtilis FtsL. However, the ftsL gene from Staphylococcus aureus (whose product has 73% of its amino acids different from those of the B. subtilis ftsL product) was not functional. We conclude that FtsL is a highly malleable protein that can accommodate a large number of sequence changes without loss of function.

Themes and variations in prokaryotic cell division

Perhaps the biggest single task facing a bacterial cell is to divide into daughter cells that contain the normal complement of chromosomes. Recent technical and conceptual breakthroughs in bacterial cell biology, combined with the flood of genome sequence information and the excellent genetic tools in several model systems, have shed new light on the mechanism of prokaryotic cell division. There is good evidence that in most species, a molecular machine, organized by the tubulin-like FtsZ protein, assembles at the site of division and orchestrates the splitting of the cell. The determinants that target the machine to the right place at the right time are beginning to be understood in the model systems, but it is still a mystery how the machine actually generates the constrictive force necessary for cytokinesis. Moreover, although some cell division determinants such as FtsZ are present in a broad spectrum of prokaryotic species, the lack of FtsZ in some species and different profiles of cell division proteins in different families suggests that there are diverse mechanisms for regulating cell division.

Control of division gene expression in Escherichia coli

Duplication of the Escherichia coli bacterial cell culminates in the formation of a division septum that splits the progenitor cell into two identical daughter cells. Invagination of the cell envelope is brought about by the co-ordinated interplay of a family of septation-specific proteins that act locally at mid-cell at a specific time in the cell cycle. The majority of the genes known to be required for septum formation are found within the large mra cluster located at 2 min on the E. coli genetic map (nucleotides 89552-107474). Examination of the controls exerted on the mra operon shows that E. coli uses an extraordinary range of strategies to co-ordinate the expression of the cell division genes with respect to each other and to the cell cycle.

Principles of macromolecular organization and cell function in bacteria and archaea

Structural organization of the cytoplasm by compartmentation is a well established fact for the eukaryotic cell. In prokaryotes, compartmentation is less obvious. Most prokaryotes do not need intracytoplasmic membranes to maintain their vital functions. This review, especially dealing with prokaryotes, will point out that compartmentation in prokaryotes is present, but not only achieved by membranes. Besides membranes, the nucleoid, multienzyme complexes and metabolons, storage granules, and cytoskeletal elements are involved in compartmentation. In this respect, the organization of the cytoplasm of prokaryotes is similar to that in the eukaryotic cell. Compartmentation influences properties of water in cells.

Bacterial cell division

Formation of the bacterial division septum is catalyzed by a number of essential proteins that assemble into a ring structure at the future division site. Assembly of proteins into the cytokinetic ring appears to occur in a hierarchial order that is initiated by the FtsZ protein, a structural and functional analog of eukaryotic tubulins. Placement of the division site at its correct location in Escherichia coli requires a division inhibitor (MinC), that is responsible for preventing septation at unwanted sites near the cell poles, and a topological specificity protein (MinE), that forms a ring at midcell and protects the midcell site from the division inhibitor. However, the mechanism responsible for identifying the position of the midcell site or the polar sites used for spore septum formation is still unclear. Regulation of the division process and its coordination with other cell cycle events, such as chromosome replication, are poorly understood. However, a protein has been identified in Caulobacter (CtrA) that regulates both the initiation of chromosome regulation and the transcription of ftsZ, and that may play an important role in the coordination process.