Reconstitution of model membranes from phospholipid and outer membrane proteins of Proteus mirabilis. Role of proteins in the formation of hydrophilic pores and protection of membranes against detergents

Potential virulence factors of Proteus bacilli

The object of this review is the genus Proteus, which contains bacteria considered now to belong to the opportunistic pathogens. Widely distributed in nature (in soil, water, and sewage), Proteus species play a significant ecological role. When present in the niches of higher macroorganisms, these species are able to evoke pathological events in different regions of the human body. The invaders (Proteus mirabilis, P. vulgaris, and P. penneri) have numerous factors including fimbriae, flagella, outer membrane proteins, lipopolysaccharide, capsule antigen, urease, immunoglobulin A proteases, hemolysins, amino acid deaminases, and, finally, the most characteristic attribute of Proteus, swarming growth, enabling them to colonize and survive in higher organisms. All these features and factors are described and commented on in detail. The questions important for future investigation of these facultatively pathogenic microorganisms are also discussed.

Enhancement of uptake of lipopolysaccharide in macrophages by the major outer membrane protein OmpA of gram-negative bacteria

Monoclonal antibodies (MAb) to lipopolysaccharide (LPS) and to the major outer membrane protein OmpA from Proteus mirabilis were generated and used to monitor the kinetics of uptake in macrophages of LPS as well as LPS bound to OmpA. Uptake was measured by a modified enzyme-linked immunosorbent assay (ELISA) in a microtiter culture system. The MAb were of various immunoglobulin G subclasses and showed strong reactivities with their antigens. Four hybridoma clones recognizing LPS and three recognizing OmpA from P. mirabilis 19 were selected for the present study on the basis of reactions in ELISA and Western blot (immunoblot) analyses. In the uptake assay, it was possible to differentiate between antigen on the cell surface and antigen which had been internalized. Uptake of LPS by macrophages was relatively rapid during the first 4 h of culture and then progressed more slowly over the remaining 24-h observation period. The level of detection of LPS in this assay system was in the nanogram range. When macrophages were pulsed with LPS for 30 min and subsequently washed to remove antigen not bound to the cells, the amount of LPS detectable on the macrophage surface decreased progressively for 3 h after the pulse, which indicated internalization of the antigen. Thereafter, LPS rose to an increased level on the cell surface. The rate of uptake of LPS was more rapid when it was in complex with OmpA. When the fate of OmpA was monitored in the same LPS-protein complexes by use of MAb to OmpA in a pulse experiment, the level of protein measured on the cell surface decreased after an initial rise, which again indicated internalization, but the protein did not reappear on the cell surface in a form detectable with the MAb. Compared with the LPS monitoring system, detection of OmpA associated with macrophages was weak, although the MAb to OmpA reacted strongly with the protein in the ELISA and Western blot analyses.

The 39-kilodalton outer membrane protein of Proteus mirabilis is an OmpA protein and mitogen for murine B lymphocytes

Partial amino acid sequence analysis of a major outer membrane protein of Proteus mirabilis (39-kDa protein) indicates that it is an OmpA protein. The mitogenic activities of the 39-kDa protein for murine lymphocytes were also investigated with T lymphocytes isolated by passing spleen cells over columns of nylon wool fiber and B lymphocytes obtained by treating spleen cells with monoclonal antibodies to Thy1 plus complement. The 39-kDa protein showed little activity in stimulating T cells to proliferate but was strongly mitogenic for B cells.

Immunochemical and biological characterization of outer membrane proteins of Porphyromonas endodontalis

Outer membrane proteins (OMP) of Porphyromonas endodontalis HG 370 (ATCC 35406) were prepared from the cell envelope fraction of the organisms. The cell envelope that had been obtained by sonication of the whole cells was extracted in 2% lithium dodecyl sulfate and then successively chromatographed with Sephacryl S-200 HR and DEAE-Sepharose Fast Flow. Two OMP fractions, OMP-I and OMP-II, were obtained, and their immunochemical properties and induction of specific antibodies were examined. The OMP-I preparation consisted of a major protein with an apparent molecular mass of 31 kDa and other moderate to minor proteins of 40.3, 51.4, 67, and 71.6 kDa, while the OMP-II preparation contained 14-, 15.5-, 27-, and 44-kDa proteins as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis. OMP-I was found to form hydrophilic diffusion pores by incorporation into artificial liposomes composed of egg yolk phosphatidylcholine and dicetylphosphate, indicating that OMP-I exhibited significant porin activity. However, the liposomes containing heat-denatured OMP-I were scarcely active. Spontaneous and antigen-specific immunoglobulin M (IgM)-, IgG-, and IgA-secreting spot-forming cells (SFC) enzymatically dissociated into single-cell suspensions from chronically inflamed periapical tissues and were enumerated by enzyme-linked immunospot assay. In patients with radicular cysts or dental granulomas, the major isotype of spontaneous SFC was IgG. In radicular cysts, the OMP-II-specific IgG SFC represented 0.13% of the total IgG SFC, while the antigen-specific IgA or IgM SFC was not observed. It was also found that none of these mononuclear cells produced antibodies specific for OMP-I or lipopolysaccharide of P. endodontalis.

Modulation of effects of lipopolysaccharide on macrophages by a major outer membrane protein of Proteus mirabilis as measured in a chemiluminescence assay

Our previous studies have shown that a major protein isolated from purified cell walls of Proteus mirabilis (39-kDa protein) is a strong modulator of the specific immune responses to lipopolysaccharide (LPS) from this bacterium. When the protein is mixed with LPS before immunization of mice, the responses of antibody-producing cells specific for LPS are greatly enhanced and converted predominantly to the immunoglobulin G isotype. In the present study, the immunomodulating effects of the 39-kDa protein were tested at the level of interaction of LPS with macrophages. Activation of macrophages was determined by measuring the production of oxygen radicals in a chemiluminescence assay with lucigenin as the amplifier. LPS from P. mirabilis induced strong oxidative metabolism in both peritoneal and bone marrow-derived murine macrophages. These responses were inhibited in a dose-dependent manner by mixing LPS with increasing amounts of the protein. In contrast, bovine serum albumin and methylated bovine serum albumin enhanced the response of macrophages dramatically when complexed with LPS. The inhibiting activity of the 39-kDa protein was also observed with LPS from Escherichia coli K-12.

Efficacy of a Proteus mirabilis outer membrane protein vaccine in preventing experimental Proteus pyelonephritis in a BALB/c mouse model

A BALB/c mouse model of nonobstructive, ascending Proteus mirabilis pyelonephritis was characterized bacteriologically, histologically, and serologically from 3 to 28 days. Intravesicular administration of 2 X 10(8) P. mirabilis K7 resulted in the septic death of 9 (16%) of 57 mice by day 15. Among the survivors, K7 colonized the kidneys in great numbers until day 21. Histological examination of the kidneys revealed acute inflammation which was characterized by neutrophil infiltration by day 3, renal necrosis by day 7, and fibroblastic infiltration by day 14 which persisted at least until day 28. The immunoglobulin G response to the outer membrane proteins (OMP) was assessed by enzyme-linked immunosorbent assay and Western blotting (immunoblotting). Anti-OMP immunoglobulin G antibodies were detected as early as day 7, and the reciprocals of their titers rose progressively up to day 28 (i.e., greater than or equal to 500). This model was also used to assess the efficacy of OMP and lipopolysaccharide (LPS) immunization in preventing renal infection. K7 OMP or LPS (100 micrograms) preparations were administered intramuscularly in Freund's complete adjuvant. After 2 weeks, mice were intravesicularly challenged with 2 X 10(8) bacteria of the homologous K7 strain or one of four heterologous strains. Compared with the saline-immunized control group and K7 LPS-immunized mice, K7 OMP recipients were protected from death when challenged by homologous or heterologous strains. In addition, K7 OMP recipients were protected (P less than 0.003) from subsequent renal infection when challenged by the K7 strain and had more rapid bacterial renal clearance when challenged by three of four heterologous strains. OMP recipients produced antibodies which bound major OMP moieties (viz., 36- to 39-kDa cell wall constituents) as assessed by Western blotting. These results support the concept that immunization with selected bacterial protein surface coat constituents can prevent uromucosal infection by interfering with colonization or renal injury.

The OmpC protein of Yersinia enterocolitica: purification and properties

OmpC, one of the major outer membrane proteins of Yersinia enterocolitica, was isolated and purified to homogeneity. When solubilized at room temperature, this protein appeared on SDS polyacrylamide gel electrophoresis as an oligomer. After heating to the temperature of boiling water, the apparent molecular weight of the monomer was 36,000. The incorporation of purified OmpC into black lipid membranes resulted in an increase in membrane conductance demonstrating pore-forming activity. The reconstituted pores exhibited the characteristics of general diffusion pores. They showed cation selectivity and had a single channel conductance of 1.3 nS in 1.0 M KCl. Assuming a constant diameter of the pore, a length of 6 nm (the width of the outer membrane) and the same ion conductivity inside and outside the pore, the diameter of the pore protein was estimated as 1.0 nm. Polyclonal antibodies were raised against the native, pore-forming protein preparation. These antibodies did not recognize the denatured form of the protein, but cross-reacted with native OmpC and OmpF of Escherichia coli. The regulation of OmpC expression in Y. enterocolitica was dependent on the osmolarity of the medium in the same way as in E. coli.

The action of LPS porins and peptidoglycan fragments on human spermatozoa

This study examines the action of the cell wall components of enterobacteria on the vitality of human spermatozoa. Lipopolysaccharides extracted from Escherichia coli K12 killed about 80% of the spermatozoa at a concentration of 50 micrograms/ml. Porins extracted from E. coli, Proteus mirabilis and Salmonella typhimurium killed between 80% and 100% of the spermatozoa at a concentration of 50 micrograms/ml. Muramic acid and N-acetylmuramic acid caused about 60% mortality at a concentration of 50 micrograms/ml. The possibility that the products of cellular lysis in the course of gram-negative infections cause temporary sterility is discussed.

The action of sodium deoxycholate on Escherichia coli

Sodium deoxycholate is used in a number of bacteriological media for the isolation and classification of gram-negative bacteria from food and the environment. Initial experiments to study the effect of deoxycholate on the growth parameters of Escherichia coli showed an increase in the lag time constant and generation time and a decrease in the growth rate constant and total cell yield of this microorganism. Cell fractionation studies indicated that sodium deoxycholate at levels used in bacteriological media interferes with the incorporation of [U-14C]glucose into the cold-trichloroacetic acid-soluble, ethanol-soluble, and trypsin-soluble cellular fractions of E. coli. Finally, sodium deoxycholate interfered with the flagellation and motility of Proteus mirabilis and E. coli. It would appear then that further improvement of the deoxycholate medium may be in order.

Identification of porins in outer membrane of Proteus, Morganella, and Providencia spp. and their role in outer membrane permeation of beta-lactams

Proteus mirabilis, Proteus vulgaris, Morganella morganii, Providencia rettgeri, and Providencia alcalifaciens, which were once classified into the same genus, Proteus, were studied. Cefoxitin-resistant mutants from these species were isolated, and it was confirmed that the resistance was attributed to the lack of an outer membrane protein, resulting in a significant decrease in the penetration of hydrophilic cephalosporins through the outer membrane. Comparison of the mutant strains with their parental strains in the diffusion rates of six monoanionic cephalosporins, a zwitterionic cephalosporin (cephaloridine), and a divalent anionic cephalosporin (cephalosporin C) suggested that each species had only one kind of porin protein, with molecular weights of 40,000 (Proteus mirabilis) or 37,000 (the other four species) and that the porins formed channels with cation selectivity, except for Proteus vulgaris. Porin proteins were purified from all the bacterial species except Providencia alcalifaciens, and the radius of the pores formed by the purified porins was estimated by the use of the liposome swelling assay. The pore radii were estimated to be approximately 0.59 nm (Proteus mirabilis), 0.63 nm (Proteus vulgaris), 0.58 nm (Providencia rettgeri), and 0.60 nm (M. morganii), similar to the size of the pore radius of Escherichia coli porins.

Outer-membrane permeability of bacteria

Gram-negative bacteria evolved to survive under the conditions in which a number of hazardous compounds are abundant. The outer membrane which protects the cell interior acts as a barrier against such hazardous agents, yet the cells must incorporate the chemicals that are essential for the cellular activity. The devices that Gram-negative bacteria developed to incorporate such essence are the transmembrane pores. These pores could be subdivided into three categories: (1) pore made of porins has a weak solute selectivity; (2) pore made of lamB protein and tsx proteins hold intermediate solute specificity. and (3) pores for the diffusion of vitamin B12 and ferric ion-chelator complexes have a tight solute specificity. Porins are identified from a number of Gram-negatives and from the outer membrane of mitochondria of various sources. Studies on the diffusion properties of these outer-membrane proteins provided essential information to understand membrane transports.

Immunoglobulin M and immunoglobulin G responses in BALB/c mice to conjugated outer membrane extracts of four Salmonella serotypes

Outer membranes (OMs) of Salmonella enteritidis, S. anatum, S. typhimurium, and S. infantis were extracted and cross-linked with glutaraldehyde to form a large macromolecular antigen. The antigen consisted of OM proteins and lipopolysaccharide and was designated 4-OMP-LPS. Polyacrylamide gel electrophoresis of extracted OMs from each serotype revealed differences in protein profiles. S. enteritidis and S. infantis possessed a greater variety of proteins than did S. anatum and S. typhimurium. Immunizations with 4-OMP-LPS in phosphate-buffered saline (4-OMP-LPS-C) and 4-OMP-LPS emulsified with muramyl dipeptide in the oil phase of a hexadecane-water emulsion (4-OMP-LPS-MDP) revealed that BALB/c mice were capable of eliciting specific primary and secondary immunoglobulin M (IgM) and IgG responses. Both antigen preparations were capable of eliciting IgM and IgG specific for the cell surfaces of each live Salmonella serotype. Also, 4-OMP-LPS-MDP and 4-OMP-LPS-C were capable of evoking a substantial anamnestic response. Adsorption studies revealed that the combined serotypes had the antigenic capacity to adsorb up to 94% of the antibodies, but 4-OMP-LPS-MDP antibodies were more effectively adsorbed than were 4-OMP-LPS-C antibodies. Adsorption of pooled antiserum with heterologous bacteria yielded a variety of adsorption profiles.

Transmembrane permeability channels across the outer membrane of Haemophilus influenzae type b

Outer membranes of Haemophilus influenzae type b were fractionated to yield Triton X-100-insoluble material and lipopolysaccharide and phospholipids. Liposomes reconstituted from lipopolysaccharide and phospholipids were impermeable to sucrose (Mr, 342) and to a high-molecular-weight dextran (average Mr, 6,600). When the Triton X-100-insoluble material was introduced into the reconstituted liposomes, the vesicles became permeable to sucrose, raffinose (Mr, 504), and stachyose (Mr, 666) and fully retained dextrans of Mr greater than 1,500. Inulin (average Mr, 1,400) was tested for its efflux from the reconstituted outer membrane vesicles; 62% of the added inulin was trapped. The molecular weight exclusion limit for the outer membrane of H. influenzae type b was therefore estimated at approximately 1,400. A protein responsible for the transmembrane diffusion of solutes was purified from H. influenzae type b by extraction of whole cells with cetyl trimethyl ammonium bromide. When this extract was passed over DEAE-Sepharose, three protein-containing peaks (I, II, and III) were eluted. Peaks I and II contained mixtures of proteins as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis; when tested for their pore-forming properties, these proteins were unable to render liposomes of lipopolysaccharide and phospholipid permeable to sucrose. Peak III contained only one molecular species of protein of molecular weight 40,000; this protein acted as a porin in reconstituted vesicles. The molecular weight exclusion limit for 40,000-molecular-weight protein matched the estimate of approximately 1,400 which was determined for outer membranes. A series of homologous saccharides of increasing degree of polymerization was prepared from agarose by hydrolysis with beta-agarase and fractionation on gel filtration chromatography. These oligosaccharides of Mr, 936, 1,242, 1,548, and 1,854 were assayed for retention by the complete vesicles containing 40-kilodalton protein and lipopolysaccharide and phospholipids. All of these oligosaccharides were lost by efflux through the porin. Since the molecular conformation of the largest oligosaccharide is an elongated semirigid helix, it is suggested that the pore formed by the 40-kilodalton protein does not act as a barrier to the diffusion of this compound.

Proteins from Salmonella R-mutants mediating protection against Salmonella typhimurium infection in mice. II. Protection tests performed with proteins free from lipopolysaccharide

Lipopolysaccharide-free proteins obtained from R-mutants of Salmonella typhimurium, S. minnesota and S. dublin as well as those from an S-form of S. typhimurium mediated protection in mice against experimental infection with S. typhimurium. The protection was measured by LD50 and is statistically significant. The level of protection of all the preparations was similar. Non-bacterial proteins had no effect under similar experimental conditions. Protection afforded by the purified proteins was lower than that of the corresponding complex crude extract; supplementation of proteins with lipopolysaccharide and phospholipids in model membrane vesicles enhanced their potency. However, lipopolysaccharides or phospholipids alone were not able to increase the efficacy of purified proteins. Some other fractions obtained by gel filtration of the crude extract also afford protection.

Porin from bacterial and mitochondrial outer membranes

The outer membrane of gram-negative bacteria acts as a molecular filter with defined exclusion limit for hydrophilic substances. The exclusion limit is dependent on the type of bacteria and has for enteric bacteria like Escherichia coli and Salmonella typhimurium a value between 600 and 800 Daltons, whereas molecules with molecular weights up to 6000 can penetrate the outer membrane of Pseudomonas aeruginosa. The molecular sieving properties result from the presence of a class of major proteins called porins which form trimers of identical subunits in the outer membrane. The porin trimers most likely contain only one large but well-defined pore with a diameter between 1.2 and 2 nm. Mitochondria are presumably descendents of gram-negative bacteria. The outer membrane of mitochondria contains in agreement with this hypothesis large pores which are permeable for hydrophilic substances with molecular weights up to 6000. The mitochondrial porins are processed by the cell and have molecular weights around 30,000 Daltons. There exists some evidence that the pore is controlled by electric fields and metabolic processes.

Fractionation of hemagglutinating and bacterial binding adhesins of Bacteroides gingivalis

An outer membrane complex containing hemagglutinating and bacterial aggregating activity has been isolated from Bacteroides gingivalis. Examination of the membrane material by biochemical analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and immunological means revealed that the crude outer membrane preparation contained three major proteins and a lipopolysaccharide population that displayed size heterogeneity. At least two membrane proteins as well as the lipopolysaccharide were found to be antigenically active by immunoblot analysis. With gel chromatography and a lipopolysaccharide disaggregating buffer the membrane material was separated into two fractions. An accompanying separation of the two adherence activities was observed. The first membrane fraction, containing mostly protein and carbohydrate material, was found to contain the bacterial aggregating activity. This fraction also contained a high-molecular-weight lipopolysaccharide population. The second membrane fraction, consisting of low-molecular-weight lipopolysaccharide, protein, and loosely bound lipid was found to contain the hemagglutinating activity.

The hemolytic effect of Salmonella typhi Ty 2 porins

Two outer membrane proteins of Salmonella typhi Ty 2 were extensively co-purified. According to their migration in dodecylsulfate/polyacrylamide gel electrophoresis and solubility characteristics, these proteins are homologous to the 35-kDa and 36-kDa porins found in Salmonella typhimurium. A porin homologous to the 34-kDa one has not been found in S. typhi Ty 2. A critical step in the purification of porins is heating at 100 degrees C in 2% sodium dodecyl sulfate before Sephadex gel filtration. The absence of detergent in aqueous suspensions enhances porin aggregation, these aggregations inducing human red cell lysis. Porins obtained by an alternative procedure consisting of heating at 60 degrees C instead of 100 degrees C were also hemolytic. Using nanomolar concentration of porins a strong influence of temperature on the hemolytic effect was observed. Porin-induced hemolysis was inhibited with anti-porin serum, as well as by a treatment with phenylglyoxal, which reacts with the arginine residues of proteins. The membrane-disrupting ability of porins aggregates might explain some pathogenic characteristics of gram-negative bacterial infections.

Escherichia coli outer membrane protein K is a porin

Protein K is an outer membrane protein found in pathogenic encapsulated strains of Escherichia coli. We present evidence here that protein K is structurally and functionally related to the E. coli K-12 porin proteins (OmpF, OmpC, and PhoE). Protein K was found to cross-react with antibody to OmpF protein and to share 8 out of 17 peptides in common with the OmpF protein. Strains that are OmpC porin- and OmpF porin- and contain protein K as their major outer membrane protein have increased rates of uptake of nutrients and a faster growth rate relative to the parental porin- strain. The protein K-containing strains are at least 1,000-fold more sensitive to colicins E2 and E3 than is the porin -deficient strain. These data suggest that protein K is a functional porin in E. coli. The porin function of protein K was also demonstrated in vitro, using black lipid membranes. Protein K increased the conductance in these membranes in discrete, uniform steps characteristic of channels with a size of about 2 nS.

Alteration of the immunoglobulin G subclass responses in mice to lipopolysaccharide: effects of nonbacterial proteins and bacterial membrane phospholipids or outer membrane proteins of Proteus mirabilis

The immunoglobulin M (IgM) and the IgG1, IgG2ab, and IgG3 subclasses of plaque-forming cells (PFC) specific for lipopolysaccharide (LPS) were measured after immunization of mice with LPS alone and compared with the responses to LPS in combination with nonbacterial proteins and with bacterial membrane phospholipid vesicles or two major outer membrane proteins from Proteus mirabilis. The relative numbers of IgG PFC belonging to the IgG1, IgG2, or IgG3 subclasses induced by immunization with LPS alone depended upon the type of LPS administered. Phospholipids and the proteins effected characteristic alterations in not only the strength but also the subclass of the IgG responses to LPS. The results suggest that the hydrophobic-hydrophilic nature or state of aggregation of the preparations plays a role in the induction of IgG1 and IgG2 subclasses of PFC specific for LPS. Complex formation with LPS and adjuvant was apparently necessary to obtain these effects.

Purification and partial characterization of the major outer membrane protein of Neisseria gonorrhoeae

A procedure is described to isolate the major outer membrane protein (protein I) from Neisseria gonorrhoeae in large quantities. The method involves precipitation of protein I by hexadecyltrimethylammonium bromide (CTB) at low ionic strength. CTB is lethal for the gonococci and solubilizes most other proteins. Protein I is brought into solution by raising the ionic strength, and the nucleic acids are subsequently removed by 20% ethanol precipitation. The CTB is removed by precipitating protein I with ethanol and replaced by N-tetradecyl-N,N-dimethyl-3-ammonia-1-propanesulfonate, a dipolar ionic detergent. Further purification is accomplished by ion-exchange and molecular sieve chromatography. Two species of protein I (34,000 daltons [34K] and 32K) were purified by these methods. The purified proteins reacted with antisera prepared against the homologous organisms. The 34K proteins I generated proteolytic fragments upon treatment with trypsin and chymotrypsin similar to those generated by 34K protein in intact gonococci. The amino acid compositions of the three proteins were much like those of other major proteins of gram-negative organisms.

Characterization of a new murein-associated lipoprotein in the outer membrane of Proteus mirabilis

A murein-associated outer membrane protein from Proteus mirabilis has been isolated. Since the protein carries ester- as well as amide-linked fatty acids it can be classified as a second outer membrane lipoprotein. An apparent molecular weight of 15,000 for this protein was determined from amino acid analysis and sodium dodecylsulfate/polyacrylamide gel electrophoresis. The amino acid composition, however, does not show similarities with the amino acid composition of the lipoprotein covalently linked to murein, which has a molecular weight of 7,300 as described previously in Proteus mirabilis.

Comparison of quantitative and qualitative antibody-producing cell responses to lipopolysaccharide in cell walls of the bacterial form and in membranes of the protoplast L-form of Proteus mirabilis

Membranes of the stable protoplast L-form of Proteus mirabilis strain VI were highly immunogenic carriers of lipopolysaccharide when compared with the immune responses to lipopolysaccharide contained in cell walls of the bacterial form of this organism.

Determination of ion permeability through the channels made of porins from the outer membrane of Salmonella typhimurium in lipid bilayer membranes

The three types of porin (matrix-proteins) from Salmonella typhimurium with molecular weights of 38,000, 39,000 and 40,000 were reconstituted with lipid bilayer membranes either as a trimer or as an oligomer (complex I). The specific conductance of the membranes increased several orders of magnitude after the addition of the porins into the aqueous phase bathing the membranes. A linear relationship between protein concentration in the aqueous phase and membrane conductance was found. In the case of lower protein concentrations (10)(-12)M), the conductance increased in a stepwise fashion with a single conductance increment of 2.3 nS in 1 M KC1. For a given salt the conductance increment was found to be largely independent of the particular porin (38 K, 39 K or 40 K) and on the state of aggregation, although porin oligomers showed an up to 10 times smaller conductance increase in macroscopic conductance measurements. The conductance pathway has an ohmic current voltage characteristic and a poor selectivity for different alkali ions. Further information on the structure of the pores formed by the different porins from Salmonella was obtained from the selectivity for various ions. From the permeability of the pore for large ions (Tris+, glucosamine+, Hepes-) a minimum pore diameter of 0.8 nm is estimated. This value is in agreement with the size of the pore as calculated from the conductance data for 1 M KC1 (1.4 nm for a pore length of 7.5 nm). The pore diameter may well account for the sugar permeability which has been found in reconstituted vesicles. The findings reported here are consistent with the assumption that the different porins form large aqueous channels in the lipid bilayer membranes and that the single conductance unit is a trimer. In addition, it is suggested that one trimer contains only one pore rather than a bundle of pores.

Isolation and partial characterization of the major outer membrane protein of Chromatium vinosum

The 42,000 major outer membrane protein of Chromatium vinosum was purified by a combination on ion-exchange chromatography, gel filtration, and isoelectric focusing. Upon isoelectric focusing, the final material produced four major hands. Three of the four bands were isolated and analyzed for similarity or differences. Protease peptide maps and cyanogen bromide maps of the three isoelectric species were identical. When the isolated isoelectric species were refocused, each produced multiple isoelectric species, suggesting that the procedure used was generating the multiple charged species. Protease treatment of the isolated outer membrane produced a 31,000 fragment from the 42,000 protein. This fragment was isolated by preparative sodium sulfate-polyacrylamide gel electrophoresis. Although the amino acid compositions of the 42,000 protein and its 31,000 trypsin fragment were different, their polarity index was the same (45%). The amino-terminal sequences of the 42,000 protein and 31,000 trypsin fragment were identical, and it concluded that the amino-terminal was buried in the membrane.

Immunological characterization of two major proteins isolated from the outer membrane of Proteus mirabilis

Two proteins with apparent molecular weights of 39,000 and 36,000 (M(r) 39,000 and M(r) 36,000, respectively) were isolated from the outer membrane of Proteus mirabilis 19. M(r) 36,000 was shown to be free of detectable amounts of the M(r) 39,000 protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and free of lipopolysaccharide according to gas chromatographic analyses of 3-hydroxymyristic acid content. The M(r) 39,000 protein contained no detectable amount of lipopolysaccharide and only a trace of M(r) 36,000. Both isolated proteins gave strong reactions in antisera produced to purified P. mirabilis 19 cell walls (outer membrane proteins in the native state). This suggested that the proteins isolated by our methods essentially retained their native configuration upon resolubilization. Antisera produced in rabbits to the isolated proteins showed strongest reactions with the homologous antigen, but some cross-reactions with the heterologous protein and with P. mirabilis 19 lipopolysaccharide were observed. These cross-reactions could be attributed to specific responses to traces of the heterologous (contaminant) proteins present in the purified proteins used as immunizing antigens. The M(r) 39,000 and M(r) 36,000 proteins have no major antigenic determinants in common. Reactions with P. mirabilis 19 lipopolysaccharide in antisera to the outer membrane proteins could be completely removed by absorption of the antisera with the M(r) 36,000 protein.

Mössbauer spectroscopic studies of iron in Proteus mirabilis

Mössbauer measurements of Proteus mirabilis cells grown in 57Fe-enriched media show that considerable quantities of iron are incorporated, particularly in the stationary phase of growth. A major part of the iron is in a form which shows magnetically split spectra at low temperatures. Fractionation of cells reveals that iron is present in both the soluble and particulate fractions, with the larger proportion being found in the soluble fraction. The iron in the particulate fraction is predominantly found in the outer membrane.

Identification of the protein producing transmembrane diffusion pores in the outer membrane of Pseudomonas aeruginosa PA01

The outer membrane of Pseudomonas aeruginosa PA01 is permeable to saccharides of molecular weights lower than about 6000. Triton X-100/EDTA-soluble outer membrane proteins were fractionated by ion-exchange chromatography in the presence of Triton X-100 and EDTA, and the protein contents of the various fractions analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Each of the major protein bands present in the Triton X-100/EDTA soluble outer membrane was separated from one another. Adjacent fractions were pooled, concentrated and extensively dialyzed to reduce the Triton X-100 concentration. Vesicles were reconstituted from lipopolysaccharide, phospholipids and each of these dialyzed fractions, and examined for their ability to retain [14C]sucrose. Control experiments indicated that the residual levels of Triton X-100 remaining in the dialyzed fractions had no effect on the formation or permeability to saccharides of the reconstituted vesicles. It was concluded that a major outer membrane polypeptide with an apparent weight of 35,000 is a porin, responsible for the size-dependent permeability of the outer membrane.

A lipopolysaccharide-binding cell-surface protein from Salmonella minnesota. Isolation, partial characterization and occurrence in different Enterobacteriaceae

1. Protein extracts obtained from Salmonella minnesota Re mutant cells by treatment with EDTA/NaC1 solution contain a protein which exhibits high affinity to bacterial lipopolysaccharides. The isolation and partial characterization of this lipopolysaccharide-binding protein is described. 2. The protein was purified from EDTA extracts by a two-step procedure consisting of ion-exchange chromatography on CM-Sephadex and preparative polyacrylamide gel electrophoresis at pH 9.5. The yield of the total purification procedure was around 16%. 3. The resulting protein preparation was homogeneous on the basis of disc gel electrophoresis, dodecylsulfate gel electrophoresis, isoelectric focusing in polyacrylamide gel and immunoelectrophoresis. 4. The isoelectric point of the protein was found to be 10.3 at 4 degrees C. Its molecular weight determined by dodecylsulfate gel electrophoresis is 15000. Its amino acid composition is characterized by the absence of histidine and proline, a low content in tyrosine and high amounts of alanine, lysine, aspartic and glutamic acid residues, or their respective amides. 5. The lipopolysaccharide-protein association was shown to be mainly due to ionic interactions of the basic protein with negatively charged groups (probably phosphate and pyrophosphate groups) of the lipid A moiety. 6. Purified lipopolysaccharide-binding protein is immunogenic in rabbits, thus enabling the preparation of specific antiserum. 7. The protein is located at the surface of Salmonella minnesota Re mutant cells as revealed by antiserum absorption with total bacteria. Ferritin-labelling studies further demonstrated that it is evenly spread over the entire cell surface. 8. Comparative antiserum absorption studies using smooth and rough strains of Salmonella minnesota, Salmonella typhimurium, Escherichia coli, Klebsiella and Shigella revealed the presence of lipopolysaccharide-binding protein (or a serologically cross-reacting antigen) in most of the strains tested. From these results the protein can be considered as a common antigen of Enterobacteriaceae.

Outer membrane proteins of smooth and rough strains of Proteus mirabilis

The outer membranes of the smooth Proteus mirabilis S1959 strain and its rough R13, R110, R51 and R45 mutants were isolated by sonication of the cells and sucrose density gradient centrifugation. The outer membrane of the rough strains had a lower density than that of their parent smooth strain, but the protein-to-phospholipid ratios were the same. The electrophoretic patterns of outer membrane polypeptides of the S and R strains in sodium dodecylsulfate/polyacrylamide gels were identical, with two major polypeptide bands, C1 and C2 (Mr 39,000 and 38,000) predominating. The C1 polypeptide band was a heat-modifiable polypeptide, which migrated as a band at Mr 33,000 when membranes were solubilized at 37 degrees C or 50 degrees C, and at Mr 39,000 when solubilization was at 100 degrees C. Susceptibility of outer membrane polypeptides to proteolytic digestion was found to be higher in isolated outer membrane preparations of the rough strains than in the smooth strain, suggesting that the availability of the polypeptide chains to proteolytic activity depends on the length of the polysaccharide chains of the outer membrane lipopolysaccharide.

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.

Interaction of lipopolysaccharide with detergents and its possible role in the detergent resistance of the outer membrane of Gram-negative bacteria

In the presence of MgCl2, amounts of detergents which disrupted phospholipid vesicles caused lipopolysaccharide I from Proteus mirabilis to aggregate and form vesicular, membrane-like structures. Vesicle formation with P. mirabilis lipopolysaccharide II containing longer O-polysaccharide chains was extremely poor. Lipopolysaccharides of Salmonella minnesota R mutants (chemotypes Ra, Rc and Re) displayed a growing tendency for vesicle formation with increasing deficiency of the R core polysaccharide. Lipopolysaccharides of chemotypes Rc and Re produced vesicles even in the absence of MgCl2 and detergent. Spherical aggregates consisting of P. mirabilis lipopolysaccharide I MgCl2 and detergent were unable to either entrap or retain [14C]-sucrose, [3H=inulin or [3H]dextran. On the other hand, S. minnesota R mutant lipopolysaccharides of chemotypes Rc and Re could entrap all three saccharides and retain them for at least short periods of time. Leakage of [3H]-inulin out of re-lipopolysaccharide vesicles was greatly retarded by addition of MgCl2 to the vesicle system. Incorporation of P. mirabilis lipopolysaccharide I or S. minnesota Rc lipopolysaccharide into phospholipid vesicles protected these model membranes from disruption by detergent. This suggested a similar protective function of lipopolysaccharide in the outer membrane of enteric bacteria against the action of surfactants occurring in their normal intestinal habitat.