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Results for “outer membrane vesicles”

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At least 19 recordsLinked to original sources
PubMed2026

Bacterial Outer Membrane Vesicles in Colorectal Cancer: Interdomain Communication Hubs in Pathogenesis and Immunotherapy.

The complex interaction between the intestinal microbiota and host mucosal immunity plays a defining role in colorectal cancer (CRC) development and therapeutic outcomes. Recently, bacterial outer membrane vesicles (OMVs)-nano-sized, lipid-bilayered extracellular particulates released by both commensal and pathogenic microorganisms-have emerged as critical long-range signaling vehicles within the gut. This review provides a comprehensive synthesis of the dual functionalities of OMVs in CRC pathogenesis and oncology. Mechanistically, pathogenic OMVs cross compromised mucosal barriers to drive horizontal gene transfer (HGT) of chimeric episomes, such as SPHINX DNAs and Bovine Meat and Milk Factors (BMMFs), thereby promoting genomic instability and neoplastic transformation. Conversely, there is a paradigm shift toward exploiting next-generation probiotic and engineered OMVs as highly tunable therapeutic platforms. By combining cutting-edge bioengineering strategies-such as biomimetic mineralization to neutralize local tissue acidity and chemotherapeutic packaging-these nanovectors effectively reprogram the immunosuppressive tumor microenvironment (TME). Specifically, optimized OMVs modulate macrophage polarization from an M2 to an M1 phenotype and stimulate CXCL10-mediated CD8+ T-cell infiltration, effectively turning immunologically "cold" tumors "hot." Finally, the great translational challenges regarding systemic endotoxicity, scalability, and target delivery, providing a strategic approach for the integration of OMV-based platforms into synergistic immune checkpoint inhibition regimens.

Colon cancer↗
PubMed1976

Identification and transmembranous localization of active cytochrome oxidase in reconstituted membranes of purified phospholipids by electron microscopy.

Cytochrome oxidase vesicles with high oxidase activity and respiratory control ratio (greater than 3.5) were characterized by the freeze-etch technique for electron microscopy. By the use of this technique, cytochrome oxidase is shown to be an inner membrane particle. By locating cross-fractured vesicles in the same preparation, cytochrome oxidase particles are shown to extend across the phospholipid bilayer membranes. When cytochrome oxidase is added to preformed liposomes respiratory control is not observed, but high oxidase activity is maintained. In this preparation the cytochrome oxidase particles are located on the outer vesicle membrane surface. These observations provide direct evidence that cytochrome oxidase is found in a transmembranous position in closed, activecytochrome oxidase vesicles having respiratory control.

Electron Transport Complex IV↗
PubMed1978

Heat-modifiable outer membrane proteins of Neisseria meningitidis and their organization within the membrane.

Neisseria meningitidis group B serotype 2 strain M986 contains two predominant outer membrane proteins, with apparent molecular weights of 41,000 (protein b) and 28,000 (protein e). Heating of outer membrane vesicles at 56 degrees C for 20 min caused much of b** to disaggregate and denature into b (41,000 daltons). In contrast, protein e could be rapidly solubilized by SDS at room temperature into its monomeric state (e*), but it was not converted to its final higher apparent molecular weight of 28,000 (e) unless heated at 100 degrees C for 2 min. We propose that protein b exists in the membrane as trimers or tetramers in a transmembrane configuration and that protein e exists as subunits on the exterior surface of the outer membrane and has a highly ordered tertiary structure.

Bacterial Proteins↗
PubMed1977

Translocation of phospholipids between the outer and inner membranes of Salmonella typhimurium.

The reversibility and specificity of phospholipid translocation between the inner and outer membrane of Salmonella typhimurium has been investigated by incorporating exogenous lipids from phospholipid vesicles into the outer membrane of intact cells. Translocation of newly incorporated phospholipids to the inner membrane was demonstrated by decarboxylation of vesicle-derived phosphatidylserine and by recovery of vesicle constituents in both inner and outer membrane fractions. All Salmonella phospholipids tested, as well as phosphatidylcholine and cholesteryl oleate were effectively translocated to the inner membrane. However, no translocation of vesicle-derived lipopolysaccharide or an incomplete biosynthetic precursor of lipid A could be detected. Translocation of phospholipids and cholesteryl ester was rapid and extensive, and appeared to lead to equilibration of the lipids between the two membranes. The mechanism of intermembrane translocation has not been established, but the results are suggestive of diffusional flow across zones of adhesion between the inner and outer membranes.

Cell Membrane↗
PubMed1977

Proline transport activity in Escherichia coli membrane vesicles of different buoyant densities.

Cytoplasmic membrane vesicles prepared by lysis of Escherichia coli W 3110 spheroplasts in a French press at 0 degrees C are heterogeneous with respect to density due to membrane protein aggregation as a result of lateral phase separation of membrane phospholipids and to the presence of more or less outer membrane. These different vesicle classes can be separated on isopycnic density gradients. Assays for various membrane-associated functions show that the membranes differ not only with respect to density and structure but also with respect to function. The proline transport system (as detected by uptake experiments with the artificial electron donor ascorbate-phenazine methosulfate) shows maximal activities in membrane fractions that have considerably higher densities than the normal cytoplasmic membrane. This is always the case, whether vesicles are isolated from membranes that exhibit a temperature-induced protein aggregation or not. A correlation between high proline transport activity and the presence of vesicles with double membranes (consisting of outer and inner membrane) has been established. The possibility that the outer membrane protects the transport system in the cytoplasmic membrane during the isolation of vesicles is discussed.

Biological Transport, Active↗
PubMed1977

Interaction of Salmonella typhimurium with phospholipid vesicles. Incorporation of exogenous lipids into intact cells.

Incubation of intact cells of Salmonella typhimurium with bilayer phospholipid vesicles results in significant transfer of vesicle lipids to the cells. The transfer requires Ca2+ or spermine, and is dependent on time, temperature, the concentration and composition of the vesicles, and the nature of the cellular lipopolysaccharide. The process results in bulk transfer of vesicle lipids to the cells rather than reciprocal molecular exchange between vesicles and the outer membrane. All components of mixed lipid vesicles, including cholesteryl oleate and lipopolysaccharide, are transferred to the cells in a ratio similar to that of the donor vesicles. The properties of the transfer process are consistent with direct fusion of vesicles with the outer membrane of the cell.

Calcium↗
PubMed1978

Outer membranes of gram-negative bacteria. XIX. Isolation from Pseudomonas aeruginosa PAO1 and use in reconstitution and definition of the permeability barrier.

A method for separating the outer and inner membranes of Pseudomonas aeruginosa PAO1 in the absence of added ethylenediaminetetraacetic acid was devised. The method yields two outer membrane fractions which show the same protein pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but differ substantially in their relative contents of phospholipids. One of these outer membrane fractions and the inner membrane fraction are less than 4% cross-contaminated, as judged by the content of typical inner and outer membrane markers. The outer membrane contains four major protein bands with apparent molecular weights of 37,000, 35,000, 21,000 and 17,000. Vesicles reconstituted from lipopolysaccharide and phospholipids were impermeable to all saccharides included in the vesicles during vesicle formation. When the vesicles contained outer membrane proteins, they fully retained only those saccharides of greater than 9,000 molecular weight, suggesting that the exclusion limit of the outer membrane of P. aeruginosa for saccharides is substantially larger than the figure (500 to 600 daltons) obtained for certain enteric bacteria. The advantages and potential disadvantages of having an outer membrane with a higher exclusion limit for hydrophilic substances are discussed.

Bacterial Proteins↗
PubMed2026

Genome-guided isolation and characterization of a novel bacteriophage infecting Escherichia coli reveal a putative new genus.

We have isolated and characterized a novel bacteriophage termed Jab, with lytic activity against multidrug-resistant clinical isolates of Escherichia coli. Phage Jab was identified from liquid manure by means of metagenome sequencing of a phage community enrichment using an E. coli clinical isolate ECH07 as host. The initial enrichment was composed of four phages, of which phage Jab represented only a minute fraction (less than 1%). Jab isolation strategy comprised a targeted approach using iterative replication rounds while equipping ECH07 with resistance against the numerically dominant phages coupled with a subsequent host switch to E. coli BL21. Whole-genome sequence analysis revealed only a remote evolutionary distance to known phages within the subfamily Vequintavirinae. The dsDNA genome of phage Jab comprises 142,100 bp (GC content 40.09%) and encodes 264 proteins and five transfer RNAs (tRNAs). No lysogeny-associated proteins were detected, suggesting an obligate lytic lifestyle. In silico genome analysis revealed the presence of at least four putative depolymerases. The closest homology of phage Jab is with members of the new genus Septuagintavirus with around 34% nucleotide identity. VIRIDIC and network analyses strongly suggest that phage Jab belongs to a putative novel genus. The host range of phage Jab is likely restricted to E. coli, displaying a moderately narrow host range (i.e., productive lysis in 8 out of 27 isolates tested). Notably, transmission electron microscopy (TEM) revealed the occurrence of conspicuous unique spherical structures attached at the end of the tail fibers when propagated on BL21 but not when propagated on ECH07. Although their function remains enigmatic, the possible role of those structures as a bacterial (vesicle-based) defense mechanism warrants further investigation.

Escherichia coli↗
PubMed2025

TamL is a Key Player of the Outer Membrane Homeostasis in Bacteroidota.

In Proteobacteria, the outer membrane protein TamA and the inner membrane-anchored protein TamB form the Translocation and Assembly Module (TAM) complex, which facilitates the transport of autotransporters, virulence factors, and likely lipids across the two membranes. In Bacteroidota, TamA is replaced by TamL, a TamA-like lipoprotein with a lipid modification at its N-terminus that likely anchors it to the outer membrane. This structural difference suggests that TamL may have a distinct function compared to TamA. However, the role of TAM in bacterial phyla other than Proteobacteria remains unexplored. Our study aimed to elucidate the function of TamL in Flavobacterium johnsoniae, an environmental Bacteroidota. Unlike its homologs in Proteobacteria, we found that TamL and TamB are essential in F. johnsoniae. Through genetic, phenotypic, proteomic, and lipidomic analyses, we show that TamL depletion severely compromises outer membrane integrity, as evidenced by reduced cell viability, altered cell shape, increased susceptibility to membrane-disrupting agents, and elevated levels of outer membrane lipoproteins. Notably, we did not observe an overall decrease in the levels of β-barrel outer membrane proteins, nor substantial alterations in outer membrane lipid composition. By pull-down assays, we found TamL co-purifying with TamB in F. johnsoniae, suggesting an interaction. Furthermore, we found that while TamL and TamB monocistronic genes are conserved among Bacteroidota, only some species encode multiple TamL, TamB and TamA proteins. To our knowledge, this study is the first to provide functional insights into a TAM subunit beyond Proteobacteria.

Bacterial Outer Membrane Proteins↗
PubMed1978

[Mitochondrial localization of cytochrome c1 with specific antibodies].

A specific antibody against cytochrome c1 (pig heart mitochondria) has been obtained. It inhibits the electron transport of the respiratory chain in the intact mitochondria at the cytochrome c1 site of inner mitochondrial membrane ; but it has no effect on the isolated submitochondrial particles (inside-out inner mitochondrial membrane vesicles free of any outer membrane or outside-out inner membrane). Thus the topologic position of cytochrome c1 in the inner mitochondrial membrane is asymetrically lcoated on the outer side of the inner mitochondrial membrane. These results agree with our previous researches on ATP-ase and cytochromes b, c and a, indicating the location on the inner side for the first one, transmembranous for the last one, on the outer side for the others respiratory chain components. Thus the electron transport from cytochrome b to a takes place in the outer region of inner mitochondrial membrane and the transmembranous location of cytochrome-oxidase facilitates the transfer of the electrons to oxygen.

Animals↗
PubMed1979

Direct evidence for formation of hybrid vesicles by fusion of plasma and outer acrosomal membranes during the acrosome reaction in boar spermatozoa.

A variety of treatment procedures was utilized to identify the origin and composition of the vesicles formed during the acrosome reaction of boar spermatozoa. Whether the acrosome reaction occurred spontaneously or was induced chemically the vesicles were hybrid vesicles composed of roughly equal proportions of plasma and outer acrosomal membranes.

Acrosome↗
PubMed1975

Cytoplasmic membrane vesicles of Escherichia coli. A simple method for preparing the cytoplasmic and outer membranes.

A simple preparative method is described for isolation of the cytoplasmic and outer membranes from E. coli. The characteristics of both membrane fractions were studied chemically, biologically, and morphologically. Spheroplasts of E. coli K-12 strain W3092, prepared by treating cells with EDTA-lysozyme [EC 3.2.1.17], were disrupted in a French press. The crude membrane fraction was washed with 3 mM EDTA-10% (w/v) sucrose, pH 7.2, and the cytoplasmic membranes and outer membranes were separated by sucrose isopycnic density gradient centrifugation. The crude membrane fraction contained approximately 10% of the protein of the whole cells, 0.3% of the DNA, 0.7% of the RNA, 0.3% of the peptidoglycan, and about 30% of the lipopolysaccharide. The cytoplasmic membrane fraction was rich in phospholipid, while the outer membrane fraction contained much lipopolysaccharide and carbohydrate; the relative contents of lipopolysaccharide and carbohydrate per mg protein in the cytoplasmic membrane fraction were 12 and 40%, respectively, of the contents in the outer membrane fraction. Cytochrome b1, NADH oxidase, D-lactate dehydrogenase [EC 1.1.1.28], succinate dehydrogenase [EC 1.3.99.1], ATPase [EC 3.5.1.3], and activity for concentrative uptake of proline were found to be localized mainly in the cytoplasmic membranes; their specific activities in the outer membrane fraction were 1.5 to 3% of those in the cytoplasmic membrane fraction. In contrast, a phospholipase A appeared to be localized mainly in the outer membranes and its specific activity in the cytoplasmic membrane fraction was only 5% of that in the outer membrane fraction. The cytoplasmic and outer membrane fractions both appeared homogeneous in size and shape and show vesicular structures by electron microscopy. The advantages of this method for large scale preparation of the cytoplasmic and outer membrane fractions are discussed.

Adenosine Triphosphatases↗
PubMed1979

Polymorphonuclear leukocyte-inhibitory factor of Bordetella pertussis. II. Localization in the outer membrane.

The outer and inner membranes and cytoplasm of spheroplasts of a strain of phase I B. pertussis were fractionated by density gradient centrifugation. The high density vesicles of the outer membranes isolated had the "Pili" characteristic of the bacteria and the same antigenicty as the bacterial surface. Activities for inhibition of polymorphonuclear leukocytes were also almost exclusively localized in this outer membrane fraction. The histamine-sensitizing activity was more dispersed, but its specific activity was also highest in the outer membrane fraction. These results suggest that molecules carrying these activities, which are probably different entities together with the tissue-adhesive pili, form a virulence complex on the surface of phase I organisms of B. pertussis.

Antigens, Bacterial↗
PubMed1977

Functional mosaicism of membrane proteins in vesicles of Escherichia coli.

Membrane vesicles of Escherichia coli prepared by osmotic lysis of lysozyme ethylenediaminetetracetate (EDTA) spheroplasts have approximately 60% of the total membrane-bound reduced nicotinamide adenine dinucleotide (NADH) dehydrogenase (ED 1.6.99.3) and Mg2+-adenosine triphosphatase (ATPase) (EC 3.6.1.3) activities exposed on the outer surface of the inner membrane. Absorption of these vesicles with antiserum prepared against the purified soluble Mg2+-ATPase resulted in agglutination of approximately 95% of the inner membrane vesicles, as determined by dehydrogenase activity, and about 50% of the total membrane protein. The unagglutinated vesicles lacked all dehydrogenase activity and may consist of outer membrane. Lysozyme-EDTA vesicles actively transported calcium ion, using either NADH or adenosine 5'-triphosphate (ATP) as energy source. However, neither D-lactate nor reduced phenazine methosulfate energized calcium uptake, suggesting that the observed calcium uptake was not due to a small population of everted vesicles. Transport of calcium driven by either NADH or ATP was inhibited by simultaneous addition of D-lactate or reduced phenazine methosulfate. Proline transport driven by D-lactate oxidation was inhibited by either NADH oxidation or ATP hydrolysis. These results suggest that the portion of the total population of vesicles capable of active transport, i.e., the inner membrane vesicles, are functionally a homogeneous population but cannot be categorized as either right-side-out or everted, since activities normally associated with only one side of the inner membrane can be found on both sides of the membrane of these vesicles. Moreover, the data indicate that oxidation of NADH or hydrolysis of ATP by externally localized NADH dehydrogenase or Mg2+-ATPase establishes a protonmotive force of the opposite polarity from that established through D-lactate oxidation.

Adenosine Triphosphatases↗
PubMed1978

Sulfide oxidation by spheroplasts of Thiobacillus ferrooxidans.

Thiobacillus ferrooxidans is an acidophilic organism important to metal leaching of low-grade ores. The aforementioned importance is related to the ability of the bacterium to oxidize reduced iron and sulfur, principally found in nature as pyrite (FeS2). The present study dealt with sulfide oxidation at low pH values and the involvement of the cell envelope in the process of the inorganic oxidations. Sulfide oxidation was noted in spheroplasts of T. ferrooxidans prepared by enzymatic and chemical treatments and partially purified by differential centrifugation. No enzyme activities were noted in membrane fractions containing enrichments of lipopolysaccharide symbolic of outer membrane material or in membrane vesicles containing (or associated with) higher levels of proteins. Results to date indicate that in an acid milieu the envelope structure containing both the outer membrane and the intact inner cytoplasmic membrane is required for sulfide oxidation.

Cell Membrane↗
PubMed1975

Light dependence of osmium reactivity in mouse photoreceptor cells.

Mouse photoreceptor cells exhibit local accumulations of osmium deposits after prolonged osmic staining at slightly elevated temperatures. Deposits were evident along the membranes of outer segment lamellae, Golgi cisternae and vesicles, nuclear envelopes, and synaptic vesicles. Other membranes within the photoreceptor cells were unreactive. No osmium reactivity was seen in other cells of the retina except for osmiophilic outer segment material which had been phagocytized by the pigment epithelium. In the outer segments, inner segments, and synaptic regions of the photoreceptor cells, the amount of osmium reactivity was increased by light stimulation and decreased following extended dark adaptation. The possible significance of the localized osmium reactivity is discussed.

Animals↗