Variant forms of matrix protein in Escherichia coli B/r bearing N plasmids

Plasmids of the N incompatibility group have been found to decrease or virtually eliminate the synthesis of the 36 500 dalton outer membrane matrix protein of their Escherichia coli B/r hosts (Iyer, R. (1977) Biochim. Biophys. Acta 470, 258–272 and Iyer, R., Darby, V. and Holland, I.B. (1978) FEBS Lett. 85, 127–132) or modify its composition. Although the 34 000 dalton tol G protein is slightly increased in some strains, it is identical in composition to the homologous protein from the plasmidless host. In three of five N⁺ strains, the synthesis of the modified matrix proteins depends on the temperature of cultivation of the strains in which they occur. The alterations to the matrix proteins are non-identical and do not affect the expression of several plasmid-coded functions including those of sensitivity to the N plasmid-specific filamentous bacteriophage IKe (Khatoon, H. and Iyer, R. (1971) Can. J. Microbiol. 17, 669–675), or their interbacterial transfer via conjugation to appropriate recipient strains. Thus, although the significance of the variant matrix proteins in N⁺ strains with respect to plasmid-mediated functions remains unclear, N plasmids nevertheless provide a convenient system which might be used to elucidate the events that precede the insertion of this protein into the outer membrane of E. coli B/r hosts.     

Cross-reactivity of major outer membrane proteins of Enterobacteriaceae, studied by crossed immunoelectrophoresis.

Outer membrane fractions were prepared from 11 bacteria in the family Enterobacteriaceae: Escherichia coli serotypes O1K-, O4K2, O26K60, O75K-, and O111K58, Shigella flexneri, Salmonella typhimurium, Klebsiella pneumonia, Serratia marcescens, Proteus vulgaris, Proteus mirabilis, and Providencia stuartii. All strains studied were found to contain one non-peptidoglycan-bound, heat-modifiable outer membrane protein, and one or two peptidoglycan-associated major outer membrane proteins in the 27,000- to 40,000-dalton range. Crossed immunoelectrophoresis using sodium dodecyl sulfate-polyacarylamide gel electrophoresis for separation of the antigens in the first dimension of the procedure was shown to provide a useful model system for studying the antigenic relationships of the major outer membrane proteins in Enterobacteriaceae species. Peptidoglycan-bound major outer membrane proteins of all bacteria studied reacted with antiserum against the purified peptidogylcan-bound matrix protein I of E. coli O26K60 in this system. Non-peptidoglycan-associated proteins of all strains cross-reacted with protein II of E. coli O26K60 in both their unmodified and their heat-modified forms. These results indicate that the genes coding for the major outer membrane proteins in the family Enterobacteriaceae have been well enough conserved during the course of evolution to allow significant antigenic cross-reactivity between the corresponding proteins in different enterobacterial species.     

Plasmid mediated alterations in composition and structure of envelopes of Escherichia coli B/r

Seven transmissible (Tra⁺), antibiotic resistance (r) plasmids, which confer sensitivity to the filamentous bacteriophage IKe on an Escherichia coli B/r strain harboring them, have been examined for the changes they evoke in the host cell membranes. The plasmids rR48and rR269, like rRM98 [1], cause a significant reduction in the density of the outer membrane and the virtual elimination of its 36 500 dalton protein. These 2 properties do not appear to be altered when rR45, rR199 or rR205 are the resident plasmids. No changes in the inner membrane proteins are seen in any of these strains. In the case of the rR46-bearing strain, the density of the outer membrane is increased and the level of the 36 500 dalton protein is unaltered; in addition, several changes in both inner and outer membrane proteins are seen. Spontaneous IKe resistant mutants isolated from strains lacking the 36 500 dalton protein are either Tra⁺ or Tra^?. Since most of them also lack this protein, the latter is not important to the expression of inter-bacterial gene transfer and IKe sensitivity.On freeze fracture, strains lacking the 36 500 dalton protein cleave almost exclusively within the outer membrane. The plasmidless host and the remaining plasmid-bearing strains show a strong fracture plane within the cytoplasmic membrane. Despite the fact that most of the plasmid-bearing strains used are proficient in effecting interbacterial plasmid transfer, no morphological differences which can be correlated with this function have been observed between their etched cell surfaces and that of the plasmidless host.     

Protein K: a new major outer membrane protein found in encapsulated Escherichia coli.

The protein composition of purified outer membranes of 47 Escherichia coli strains was examined by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis. Of 33 encapsulated strains, all contained an outer membrane protein distinguishable from previously reported proteins. The 14 non-encapsulated strains with one exception lacked this protein. Because of its apparent association with encapsulation (K antigen) we have named it K protein. The protein was purified nearly to homogeneity by chromatography in the presence of detergents, and its composition was determined. Its amino acid composition does not differ significantly from that reported for protein I, another E. coli major outer membrane protein. Furthermore, the N-terminal amino acid sequence of protein K indicates that it is related to protein I.     

Isolation and partial characterization of protein E, a major protein found in certain Escherichia coli K-12 mutant strains: relationship to other outer membrane proteins.

Escherichia coli outer membrane protein E was purified, and its amino acid composition and N-terminal amino acid were determined. The purified protein was shown to be immunologically and electrophoretically identical to proteins Ic (U. Henning, W. Schmidmayr, and I. Hindennach, Mol. Gen. Genet. 154:293-298, 1977) and e (W. van Alphen, N. van Selm, and B. Lugtenberg, Mol. Gen. Genet. 159:75-83, 1978). Proteins E, e, and Ic were also immunologically related to E. coli outer membrane protein Ia. Lugtenberg and co-workers (B. Lugtenberg, R. van Boxtel, C. Verhoef, and W. van Alphen, FEBS Lett. 96:99-105, 1978) have shown that electrophoretically identical peptides were generated by cyanogen bromide treatment of proteins E, e, and Ic.     

Delivery of protein antigens and DNA by virulence-attenuated strains of Salmonella typhimurium and Listeria monocytogenes

Two different plasmid-vector systems were developed which allow the efficient production and presentation of protein antigens in antigen-presenting cells (APC) by means of virulence-attenuated bacteria. The first antigen-delivery system is based on the secretion machinery of the Escherichia coli hemolysin (HlyA-type I secretion system), which transports proteins, possessing the specific HlyA secretion signal (HlyA(s)) at the C-terminus, across both membranes of gram-negative bacteria. This system functions in all gram-negative bacteria that possess the TolC-analogous protein in the outer membrane. This outer membrane protein is necessary for the stable anchoring of the type I secretion apparatus in the cell envelope. Suitable HlyA(s)-fused antigens are secreted with high efficiency by E. coli and by virulence-attenuated strains of Salmonella, Shigella, Vibrio cholerae and Yersinia enterocolitica. The other vector system expresses the heterologous antigen under the control of an eukaryotic promoter in a similar fashion as in plasmids commonly used for vaccination with naked DNA. This plasmid DNA is introduced into APCs with the help of virulence-attenuated self-destructing Listeria monocytogenes mutants. After synthesis of the heterologous protein, epitopes of the antigen are presented by the APC together with MHC class I molecules. This system functions in macrophages and dendritic cells in vitro and can also be used in a modified form in animal models.     

Detection of Shiga-like toxin on the outer membranes of Shigella species and Escherichia coli K-12

Abstract Outer membranes of Shigella species and E. coli K-12 carrying large invasive plasmids and isogenic non-invasive strains without plasmids were analyzed by SDS-PAGE. The immunoblotting analysis of the outer membrane proteins of these bacteria was performed with monoclonal antibody (mAb) made against A and B subunits of Shiga-like toxin (SLT). The SLT was detected in the outer membranes of S. dysenteriae 1 IDBM11, S. sonnei PNS20, S. flexneri M90T, S. dysenteriae 60R, and E. coli K-12 strain AB2463. The two other E. coli K-12 strains, C600 and 933J were included as controls for low and high toxin producers respectively. The outer membrane protein band of molecular weight 70 kDa was common to all bacterial strains studied. The most prominent band of 70 kDa protein was seen to be present in the high toxin producing plasmidless strain of S. dysenteriae 60R and the lysogenic strain of E. coli 933J. The invasive strains of S. dysenteriae 1 and S. flexneri M90T which carry the large invasive plasmids showed the least prominent band of 70 kDa protein.
The immunoblotting analysis of Shiga-toxin partially purified from the S. dysenteriae 60R strain revealed the absence of 70 kDa band on SDS-PAGE, instead the two dissociated subunits were seen. Furthermore, periplasmic Shiga-toxin proteins also showed the complete dissociation into A and B subunits. However, under the same denaturing conditions, the 70 kDa protein band cross-reacting with mAb against A and B subunits was still present in the outer membranes of all different strains.     

Caulobacter crescentus cell envelope: effect of growth conditions on murein and outer membrane protein composition

The murein and membrane protein compositions of Caulobacter crescentus strains CB13B1a and CB15 have been characterized, and the influence on cell envelope constituents of culture conditions which affect morphogenesis have been studied. Amino acid and sugar analysis of murein sacculi revealed a simple A1gamma murein configuration typical of gram-negative bacteria. The membranes of C. crescentus had low levels of 2-keto-3-deoxyoctonate relative to enteric bacteria, in addition to the absence of lipid A components (Shapiro et al., Science 173:884-892, 1971; Chow and Schmidt, J. Gen. Microbiol, 83:369-373, 1974). Nevertheless, C. crescentus membranes could be fractionated into inner and outer membrane components by sucrose density gradient centrifugation procedures developed for Escherichia coli. The proteins of the outer membrane were distributed between three major (I, II, and III) and two minor (IV and V) protein classes. Class I proteins were greater than or equal to 74,000 daltons and constituted the primary proteins of the outer membrane. Class I proteins were separated into approximately 50 polypeptides by two dimensional gel electrophoresis; the protein composition of thi s class was affected by culture conditions in both CB13B1a and CB15. Class II (47,000 to 39,000 daltons) and III (20,000 to 11,500 daltons) proteins differed in each strain in composition and response to culture conditions.     

Fuctional organization of the outer membrane of escherichia coli: Phage and colicin receptors as components of iron uptake systems

The functional interaction of outer memberane proteins of E. coli can be studied using phage and colicin receptors which are essential components of penetration systems. The uptake of ferric iron in the form of the ferrichrome complex requires the ton A and ton B functions in the outer membrane of E. coli. The ton A gene product is the receptor protein for phage T5 and is required together with the ton B function by the phages T1 anf ?80 to infect cells and by colicin M and the antibiotic albomycin, a structural analogue of ferrichrome, to kill cells. The ton B function is necessary for the uptake of ferric iron complexed by citrate. Iron complexed by enterochelin is only transported in the presence of the ton B and feu functions. Cells which have lost the feu function are resistant to the colicins B, I or V while ton B mutants are resistant to all colicins. The interaction of the ton A, Ton B, and feu functions apparently permits quite different “substrates” to overcome the permeablility barrier of the outer membrane. It was shown for ferrichrome dependent iron uptake that the complexing agent was not altered and could be used repeatedly. Only very low amounts of ³H-labeled ferrichrome were found in the cell. It is possible that the iron is mobilized in the membrane and that desferriferrichrome is released into the medium without having entered the cytoplasm. Growth on ferrichrome as the sole iron source waw used to select revertants of T5 resistant ton A mutants. All revertants exhibited wild-type properties with the exception of partial revertants. In these 4 strains, as in the ton A mutants, the ton A protein was not detectable by SDS polyacrylamide gel electrophoreses of outer membranes. Albomycin resistant mutants were selected and shown to fall into 5 categories: (1) ton A; (2) ton B mutants; (3) mutants with no iron transport defects and normal ton A/ton B functions, which might be target site mutants; (4) mutants which were deficient in ferrichrome-mediated iron uptake but had normal ton A/ton B functions. We tentatively consider that the defect might be located in the active transport system of the cytoplasmic membrane; (5) a variety of mutants with the following general properties: most of them were resistant to colicin M, transported iron poorly, and, like ton B mutants, contained additional proteins in the outer membrane. The outer membrane protein patterns of wild-type and ton B mutant strains were compared by slab gel electrophoresis in an attempt to identify a ton B protein. It was observed that under most growth conditions, ton B mutants overproduced 3 proteins of molecular weights 74,000–83,000. In extracted, iron-deficient medium, both the wild-type and ton B mutant strains had similar large amounts of these proteins in their outer membranes. The appearance of these proteins was suppressed by excess iron in both wild-type and mutant. From this evidence it is apparent that the proteins appear as a response to low intracellular iron rather than being controlled by the ton B gene. The nature of these proteins and their possible role in iron transport is disussed.     

Outer Membrane Proteins of Escherichia coli VII. Evidence That Bacteriophage-Directed Protein 2 Functions as a Pore

Protein 1, a major protein of the outer membrane of Escherichia coli, has been shown to be the pore allowing the passage of small hydrophilic solutes across the outer membrane. In E. coli K-12 protein 1 consists of two subspecies, 1a and 1b, whereas in E. coli B it consists of a single species which has an electrophoretic mobility similar to that of 1a. K-12 strains mutant at the ompB locus lack both proteins 1a and 1b and exhibit multiple transport defects, resistance to toxic metal ions, and tolerance to a number of colicins. Mutation at the tolF locus results in the loss of 1a, in less severe transport defects, and more limited colicin tolerance. Mutation at the par locus causes the loss of protein 1b, but no transport defects or colicin tolerance. Lysogeny of E. coli by phage PA-2 results in the production of a new major protein, protein 2. Lysogeny of K-12 ompB mutants resulted in dramatic reversal of the transport defects and restoration of the sensitivity to colicins E2 and E3 but not to other colicins. This was shown to be due to the production of protein 2, since lysogeny by phage mutants lacking the ability to elicit protein 2 production did not show this effect. Thus, protein 2 can function as an effective pore. ompB mutations in E. coli B also resulted in loss of protein 1 and similar multiple transport defects, but these were only partially reversed by phage lysogeny and the resulting production of protein 2. When the ompB region from E. coli B was moved by transduction into an E. coli K-12 background, only small amounts of proteins 1a and 1b were found in the outer membrane. These results indicate that genes governing the synthesis of outer membrane proteins may not function interchangeably between K-12 and B strains, indicating differences in regulation or biosynthesis of these proteins between these strains.     

Release of a special fraction of the outer membrane from both growing and phage T4-infected Escherichia coli B.

Growing Escherichia coli release envelope material into the medium. Upon infection with T4 phage increased amounts of this material are released and at a greater rate. In order to determine whether both inner and outer membranes are present in this material, and whether the material released by growing cells differs from that released by infected cells, we have examined the protein composition of envelope released by growing and T4-infected E. coli B. Our results show: (a) the protein composition of envelope released from growing or infected cells is similar, (b) the proteins present are representative of the outer membrane, (c) the major outer membrane protein of E. coli B, protein II, is deficient in the released material. We therefore conclude that the envelope material released from growing or infected E. coli represents a special fraction of the outer membrane. This finding is discussed in relation to outer membrane structure and function. In addition, data are presented on the differing outer membrane protein composition of substrains of E. coli B obtained from different laboratories.     

Purification of protein A, an outer membrane component missing in Escherichia coli K-12 ompA mutants.

Outer membrane materials prepared from an Escherichia coli ompA (tolG) strain do not contain one of the major outer membrane proteins found in ompA+ strains. This protein has been purified in high yield from detergent-solubilized cell envelope material prepared from an ompA+ strain by preparative electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate. The purified protein is homogeneous in three electrophoretic systems, contains 2 mol of reducing sugar/mol of peptide and has alanine as the N-terminal amino acid. The amino acid composition is nearly identical to outer membrane protein II or B purified by others from incompletely solubilized cell envelope material. Thus, the fraction of outer membrane protein II or B that is difficult to solubilize is identical with the more readily solubilized fraction.     

Separation and characterization of the outer membrane of Pseudomonas aeruginosa.

A method is described for the preparation of outer and cytoplasmic membranes of Pseudomonas aeruginosa, and the outer membrane proteins characterized. Isolated outer and cytoplasmic membranes differed markedly in the content of 2-keto-3-deoxyoctonate (lipopolysaccharide) and phospholipid as well as in the localization of certain enzymes (NADH oxidase, succinate dehydrogenase, D-lactate dehydrogenase, malate dehydrogenase, and phospholipase), and also in the microscopic morphology. The outer membrane preparation showed activity neutralizing a certain bacteriocin or bacteriophages, whereas the cytoplasmic membrane preparation showed no neutralizing activity. The protein composition of membrane preparations from five different strains of P. aeruginosa [P14, M92 (PAO1), PAC1, P15, and M2008 (PAT)] were determined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. More than 50 protein bands were detected in the cytoplasmic membrane preparation. The protein compositions of outer membranes from the five different strains were very similar: at least 6 major bands were found (apparent molecular weights: Band D, 50,000; band E, 45,000; band F, 33,000; bands G and H, 21,000; and band I, 8,000). The protein composition of outer membranes was affected by some physiological growth conditions. Some features of major outer membrane proteins were also studied. Band F showed anomalous migration on SDS polyacrylamide gel electrophoresis depending on the solubilizing conditions or pretreatment with TCA. Band I seemed to be a protein analogous to the lipoprotein which had been found in the outer membrane of Escherichia coli.     

Regulation of the synthesis of surface protein in the cell cycle of E. coli B/r.

We have studied the biogenesis of the envelope of E. coli B/r by measuring the synthesis of protein in separated inner and outer membranes during the cell cycle. While total protein and bulk inner membrane protein were synthesized continuously and at an exponentially increasing rate throughout the cycle, bulk outer membrane protein was synthesized at a constant rate throughout the cycle with an abrupt doubling in rate occurring 10–15 min before division. A similar pattern was observed when the rate of synthesis of an individual protein, the 36.5K outer membrane protein, was measured directly in total cell lysates. Neither thymine starvation nor changes in gene dosage of exponential cultures affected the synthesis of outer membrane protein, indicating that the doubling in rate is not controlled by a gene duplication mechanism. Other findings, however, further indicate that outer membrane protein synthesis is regulated in some way. Thus the concentration of 36.5K porin per unit surface area remained constant as the surface area/volume ratio varied widely with growth rate. We also obtained direct evidence for an overall limitation on the rate of synthesis of bulk outer membrane proteins; when a new class of outer membrane proteins was induced, the rate of synthesis of other surface proteins was correspondingly reduced. On the basis of these results, we discuss a model in which the linear growth of outer membrane protein results from a limitation of outer membrane polypeptide synthesis at the translational level, reflecting the linear expansion of the underlying peptidoglycan layer in the envelope.     

Isolation and characterization of a new type of Escherichia coli K12 phoB mutants

A new type of Escherichia coli K12 phoB mutant was isolated as 5-fluorouracil-plus-adenosine-resistant derivatives of a upp phoS,T strain. Such phoB mutants (called type III) differ from previously described phoB mutants (types I and II) in the synthesis pattern of phosphate-regulated periplasmic proteins P4a and 30.5 K, sensitivity to toxic compounds, and several other phenotypic characters. The analysis of isogenic strains carrying phoB mutations (type I, II or III) showed that; the phoB gene product exerted (i) a positive control over the synthesis of periplasmic proteins 30.5 K, 11.5 K, and 9 K, inner membrane proteins 32 K and 17.5 K, and outer membrane protein Tsx, (ii) and a direct or indirect negative control over the synthesis of a 20 K phosphate-inducible periplasmic protein.     

Oscillations in the synthesis of cell wall components in synchronized cultures of Escherichia coli.

The rate of cell wall synthesis with respect to both proteins and lipids was determined in synchronized cultures of Escherichia coli B/r. Whereas the rate of total protein synthesis showed an exponential increase with cell age, the rate of incorporation of proteins and lipids into cell wall had a maximum at a cell age of 30 to 35 min, 15 min before cell division. This oscillation was observed in both the cytoplasmic membrane and in the outer membrane of the cell envelope.     

Protein II influences ferrichrome-iron transport in Escherichia coli K12.

Ferrichrome-promoted iron uptake in Escherichia coli K12 is strictly dependent upon the tonA gene product, a 'minor' outer membrane protein. By selection for mutants of E. coli resistant to phages which require 'major' outer membrane proteins as receptors, strains with pronounced protein deficiencies were constructed. Such strains were tested for anomalous behaviour of ferrichrome transport. No significant differences in iron uptake were detected in E. coli K12 strains with markedly reduced amounts of protein I. However, a reduction in the initial velocity (up to 40%) was observed in E. coli deficient in outer membrane protein II. This difference was only evident when cells were grown under iron-starvation conditions; it was abolished when cells were grown in rich medium. Kinetic parameters for ferrichrome transport were determined for maximum velocity but for Km; double reciprocal plots showed a biphasic nature, probably attributable to a limited number of outer membrane binding sites and to the multi-component nature of the ferrichrome-iron transport system.     

Membrane proteins correlated with expression of the polysialic acid capsule in Escherichia coli K1.

Growth of Escherichia coli K1 strains at 15 degrees C results in a defect in the synthesis or assembly of the K1 polysialic acid capsule. Synthesis is reactivated in cells grown at 15 degrees C after upshift to 37 degrees C, and activation requires protein synthesis (Whitfield et al., J. Bacteriol. 159:321-328, 1984). Using this temperature-induced defect, we determined the molecular weights and locations of membrane proteins correlated with the expression of K1 (polysialosyl) capsular antigen. Pulse-labeling experiments demonstrated the presence of 11 proteins whose synthesis was correlated with capsule appearance at the cell surface. Using the differential solubility of inner and outer membranes in the detergent Sarkosyl, we localized five of the proteins in the outer membrane and four in the inner membrane. The subcellular location of two of the proteins was not determined. Five proteins appeared in the membrane simultaneously with the initial expression of the K1 capsule at the cell surface. One of these proteins, a 40,000-dalton protein localized in the outer membrane, was identified as porin protein K, which previously has been shown to be present in the outer membrane of encapsulated E. coli. The possible role of these proteins in the synthesis of the polysialosyl capsule is discussed.     

Intermediate location in the assembly of the matrix protein or porin into the outer membrane of Escherichia coli.

Evidence from pulse-chase experiments indicates that the outer membrane matrix protein or porin of Escherichia coli B/r passes through a Sarkosyl-soluble membrane pool on the way to its eventual Sarkosyl-insoluble state in the outer membrane.     

Mutations in genes cpxA and cpxB alter the protein composition of Escherichia coli inner and outer membranes.

Mutations in chromosomal genes cpxA and cpxB altered the protein composition of the inner and outer bacterial membranes. Electrophoretic analyses of membrane proteins from isogenic strains differing only at their cpx loci and of spontaneous cpxA+ revertants of a cpxA cpxB double mutant showed that the alterations define a pattern that is uniquely attributable to the cpx mutations. Two major outer membrane proteins, the OmpF matrix porin and the murein lipoprotein, were deficient or absent from the outer membrane of mutant cells, whereas the quantities of two other major outer membrane proteins, the OmpC matrix porin and the OmpA protein, were not significantly altered. The cpx mutations did not generally alter the functional or chemical properties of the cell envelope. In the electron microscope, mutant cells appeared ovoid, but individual cells showed no surface irregularities to suggest gross defects in the cell envelope. These observations suggest that the primary effect of the mutations is to alter selectively the synthesis or translocation of certain envelope proteins.