Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P43026 (lipopolysaccharide)
 62,215 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The conductance properties of three members of the porin family which form channels across the outer membrane of Gram-negative bacteria were compared. With their endogenous lipopolysaccharide (LPS) bound, the closely related porins F and C from Escherichia coli reveal significantly different conductance steps and closing potentials, with values of 0.82 nS (nanosiemens) and 89 mV for F-type channels, and 0.49 nS and 158 mV for C-type pores (1 M NaCl), respectively. On the basis of their closing potentials, the two channel types can be distinguished unequivocally. If reconstituted in asolectin and extraneous LPS, porin C forms F-type in addition to C-type channels. Substitution of asolectin by mitochondrial lipids yields the native C-type pores only. Both channel types can be induced to assume the mutually other channel configuration by variation of ionic strength. A multiplicity of channel subtypes is observed by variation of the pH of the medium. The three channels within a trimer are, however, consistently of the same type. Since structural studies have revealed a single channel per monomer, the several conductance steps observed are likely to reflect distinct configurations of the same channel. Best channel recoveries were observed if endogenous LPS remained associated to porin during purification. Significant yields could nevertheless be obtained also if LPS was removed from porin and replaced with various precursors or chemically synthesized analogues. As function requires the presence of glycolipids, yet crystallization is perturbed by heterodisperse endogenous LPS, the smallest monodisperse analogues yielding good channel recovery were determined. The minimal synthetic moiety is a monoglucosaminetetraacyl compound. The characteristics of porin B from E. coli BE are shown to be indistinguishable from those of porin F. The conductance properties of this porin, refolded from random coil configuration, are indistinguishable from those exhibited by native protein. The formation of channels is thus encoded by the sequence of the mature polypeptide alone.
 ...
PMID:Plasticity of Escherichia coli porin channels. Dependence of their conductance on strain and lipid environment. 172 4

The assembly of outer membrane proteins of Escherichia coli was examined using the OmpF porin as a model. Since this protein is made as a precursor, which is processed to a protein of Mr 37,000 before being assembled into trimers in the outer membrane, we synthesized a modified OmpF, which lacked 16 out of 22 amino acid residues from its signal sequence, in a coupled transcription-translation system. This modified protein resembled the unfolded, monomeric OmpF in its electrophoretic behavior, but much of the protein apparently existed in a more tightly folded conformation as it was recognized by a monoclonal antibody specific to a surface epitope of the native, trimeric OmpF porin. At least some conformers of this protein could be further incorporated into outer membrane or lipopolysaccharide bilayers, and assembled into trimers. The trimers formed were trypsin-resistant and heat-stable in sodium dodecyl sulfate up to 70 degrees C, thus showing the characteristics of the native trimeric protein. These results extend our earlier observation that OmpF monomer secreted by spheroplasts of E. coli can be trimerized in vitro (Sen, K., and Nikaido, H (1990) Proc. Natl. Acad. Sci. U.S. A 87, 743-747) and show that the trimerization can occur, albeit at a low efficiency, with porin monomers synthesized in vitro, presumably not contaminated by membrane fragments or other components of the cell envelope. However, comparison of trimerization efficiency of the nascent in vitro product with that of the same product already exposed to aqueous medium, as well as with that of the spheroplast-secreted product, leads us to the working hypothesis that the trimerization process in intact cells is accelerated either by accessory components or by the conformational changes accompanying the secretion through the cytoplasmic membrane and that the reactions observed in this study represent only part of the physiological process.
 ...
PMID:Trimerization of an in vitro synthesized OmpF porin of Escherichia coli outer membrane. 204 Jun 34

A Pseudomonas aeruginosa (isolate 416) from a patient with pneumonia, was initially susceptible to imipenem (MIC: 2 mg/l) but became resistant to this antibiotic (isolate 470, MIC: 32 mg/l) during imipenem therapy. Treatment failed. No parallel increases in MIC were observed for other antimicrobials tested. Isolates 416 and 470 shared the same pyocin type and serotype, produced small amounts of an inducible beta-lactamase, and had similar lipopolysaccharide compositions. On electrophoresis of outer membrane proteins, the porin F, identified by the monoclonal antibody MA4-4, was expressed similarly by the two isolates but the production of one band (apparent molecular weight: 47,000) was diminished in isolate 470. [14C]-Imipenem labelling of intact cells proceeded more slowly in 470 than in 416, especially when bacterial cells were treated by antibody MA4-4 to block the porin F channel. [14C]-Imipenem labelling of penicillin binding proteins (PBP) showed that the band identified as PBP-4 bound markedly less radioactivity in isolate 470 than in 416. After isolate 470 was passaged several times in antibiotic-free broth, the imipenem MIC was decreased from 32 to 8 mg/l, and the [14C]-imipenem PBP pattern recovered the initial profile as exhibited by isolate 416. Two resistance mechanisms, affecting imipenem electively, could have combined their effect in the post-therapy isolate, altered target protein and reduced permeability.
 ...
PMID:Novel resistance to imipenem associated with an altered PBP-4 in a Pseudomonas aeruginosa clinical isolate. 210 15

A large-scale purification scheme was developed for lipopolysaccharide-free protein P, the phosphate-starvation-inducible outer-membrane porin from Pseudomonas aeruginosa. This highly purified protein P was used to successfully form hexagonal crystals in the presence of n-octyl-beta-glucopyranoside. Amino-acid analysis indicated that protein P had a similar composition to other bacterial outer membrane proteins, containing a high percentage (50%) of hydrophilic residues. The amino-terminal sequence of this protein, although not homologous to either outer membrane protein, PhoE or OmpF, of Escherichia coli, was found to have an analogous protein-folding pattern. Protein P in the native trimer form was capable of maintaining a stable functional trimer after proteinase cleavage. This suggested the existence of a strongly associated tertiary and quaternary structure. Circular dichroism studies confirmed these results in that a large proportion of the protein structure was determined to be beta-sheet and resistant to acid pH and heating in 0.1% sodium dodecyl sulphate.
 ...
PMID:Large-scale purification and biochemical characterization of crystallization-grade porin protein P from Pseudomonas aeruginosa. 245 38

IgG antibody to the outer membrane of Pseudomonas cepacia was quantified in sera from controls without cystic fibrosis (CF) and from Pseudomonas aeruginosa- and P. cepacia-infected and noninfected patients with CF. The mean antibody titer in the P. cepacia-infected group was significantly higher than that in the other three groups; the mean titer in the P. aeruginosa-infected group was significantly higher than that in the noninfected and control groups. Preabsorption of CF sera with P. cepacia outer membrane produced a significantly lower mean antibody concentration than did matched samples preabsorbed with an equal amount of lipopolysaccharide. By western blot, significantly more P. cepacia-infected patients produced IgG to the 27- than the 36-kilodalton (kDa) porin protein of P. cepacia; 12 of 16 P. aeruginosa-infected patients produced IgG to the 27-kDa porin. Sera from all patients in both groups contained IgG to the porin protein of P. aeruginosa by western blot. We conclude that the 27-kDa porin of P. cepacia is antigenic in most P. cepacia-infected patients with CF and that some P. cepacia outer membrane components may be antigenically related to those of P. aeruginosa.
 ...
PMID:Serum IgG antibody to outer membrane antigens of Pseudomonas cepacia and Pseudomonas aeruginosa in cystic fibrosis. 245 19

Restoration of IgG antibody binding to heat-denatured meningococcal outer membrane proteins has been studied on immunoblots with a series of 14 detergents. Nitrocellulose strips with the blotted proteins were incubated with the detergents and sera from human volunteers vaccinated with meningococcal membrane proteins. Zwitterionic and ionic detergents, containing substituted quarternary ammonium or amino groups with a minimum of 10 C atoms in the alkyl chain, restored the antigenicity of the serotype-specific class 2 porin protein. The concentrations of the Zwittergent detergents necessary for activation decreased with increasing alkyl chain length of the homologues. Only zwitterionic detergents renatured the class 1 protein. Both proteins were weakly antigenic in the presence of the nonionic detergents Triton X-100 and Tween 20. Meningococcal lipopolysaccharide restored antibody binding to the porin, but not to the class 1 protein. Similar concentrations of lipopolysaccharides from two other gram-negative bacteria had no effect.
 ...
PMID:Restoration of antibody binding to blotted meningococcal outer membrane proteins using various detergents. 245 53

Porin is a trimeric membrane protein that functions as a diffusion pore in the outer membrane of Escherichia coli. We report the existence and purification of porin heterotrimers between the ompC, ompF, and phoE porin gene products. Separation was achieved using a high resolution anion exchange column. The amount of each heterotrimer species present depended on the level of expression of the subunits and was consistent with random mixing of trimer subunits. A strong effect of bacterial lipopolysaccharide on the chromatography of porin was also detected. These results imply that assembly of porin trimers occurs between subunits synthesized on different polysomes and that subunit contacts between the porin subunits occur in conserved regions of the primary sequence.
 ...
PMID:Existence and purification of porin heterotrimers of Escherichia coli K12 OmpC, OmpF, and PhoE proteins. 246 93

The outer membrane of Campylobacter coli, C. jejuni and C. fetus cell envelopes appeared as three fractions after sucrose gradient centrifugation. Each outer membrane fraction was contaminated with succinate dehydrogenase activity from the cytoplasmic membrane fraction. Similarly the inner membrane fraction was contaminated with 2-ketodeoxyoctonate and outer membrane proteins including the porin(s). The separation of these two membranes was not facilitated by variations in lysozyme treatment, cell age, presence or absence of flagella, or longer lipopolysaccharide chain length. Sodium lauroyl sarcosinate extraction resulted in an outer membrane fraction which contained some inner membrane contamination and produced multiple bands upon sucrose gradient centrifugation. Triton X-100 extraction removed the inner membrane from the outer membrane and Triton X-100/EDTA treatment extracted lipopolysaccharide-rich regions of the outer membrane which contained almost exclusively the Campylobacter porin(s). These data indicated that the inner and outer membranes of the Campylobacter cell envelope were very difficult to separate, possibly because of extensive fusions between these two membranes.
 ...
PMID:Comparison of methods used to separate the inner and outer membranes of cell envelopes of Campylobacter spp. 247 28

Two sets of monoclonal antibodies (MoF type I and MoF type II) directed against the OmpF protein were used to analyze the immunological reactivity of the major outer membrane porins of E. coli B and K-12. All these antibodies present a specificity to the native OmpF protein. In addition, among the type II antibodies, MoF 18, 19 and 20 could recognize an epitope present on both monomeric and trimeric forms of the porin as demonstrated by immunoblotting analyses. The use of two different screening methods led to the isolation of two different sets of MoF, one specific for a native conformation accessible only on E. coli B strain and the second directed against epitopes present on OmpF of the two strains, B and K-12. These various responses are discussed in relation to the lipopolysaccharide binding to OmpF and with respect to the screening test used.
 ...
PMID:Immunological analysis of porin polymorphism in Escherichia coli B and K-12. 248 21

Pseudomonas aeruginosa PAO1 was grown in vivo in chambers implanted into the peritoneums of mice and rats. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of extracts of bacterial cells taken from the chambers and washed to remove loosely bound host proteins revealed the presence of the major outer membrane proteins D2, E, F, G, and H2. Western immunoblotting with specific antisera confirmed the presence of porin protein F and lipoprotein H2. However, there was no apparent induction of the phosphate starvation-inducible porin P or the divalent cation starvation-inducible protein H1. Small amounts of proteins with molecular weights similar to those of the iron-regulated outer membrane proteins were found in cells grown in vivo; however, their presence could not be confirmed immunologically. The presence of pili and flagella on the cells grown in vivo was demonstrated by electron microscopy and Western immunoblotting. A consistent alteration in the lipopolysaccharide banding pattern was observed after growth in vivo. Compared with cells of strain PAO1 grown in vitro, cells grown in vivo appeared to lack a series of high-molecular-weight O-antigen-containing lipopolysaccharide bands and gained a new series of lower-molecular-weight lipopolysaccharide bands. This alteration in the lipopolysaccharide after growth in vivo did not affect the O-antigen serotype or the resistance of the bacteria to serum.
 ...
PMID:Surface characteristics of Pseudomonas aeruginosa grown in a chamber implant model in mice and rats. 249 57


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>