Chemical heterogeneity of major outer membrane pore proteins of Escherichia coli

Genetic analysis of bacteriophage N4 adsorption

We isolated six mutants of Escherichia coli K-12 that were defective in bacteriophage N4 adsorption. We mapped the mutations to four loci designated nfrA through nfrD (N four resistance). nfrA and nfrB were tightly linked to each other and were mapped to min 12 of the E. coli linkage map. nfrC was mapped to min 85, and nfrD was mapped between min 44 and 58. We isolated a clone carrying both nfrA and nfrB and identified its gene products through maxicell analysis of plasmid subclones. The nfrA gene product was an outer membrane protein of 96,000 apparent molecular weight, whereas nfrB encoded an inner-membrane protein of 69,500 apparent molecular weight. The nfrB1 mutation did not affect the export of the nfrA gene product to the outer membrane and did not affect the alkaline phosphatase activity of an nfrA-phoA fusion. We propose that nfrA encodes the structural receptor for N4 and that the nfrB gene product may be required for irreversible adsorption and injection of the phage genome and virion-encapsulated RNA polymerase through the inner membrane.

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.

Characterisation of channels induced in planar bilayer membranes by detergent solubilised Escherichia coli porins

Purified OmpF, OmpC, NmpC, PhoE and Lc (Protein 2) porins from the Escherichia coli outer membrane were incorporated into planar phospholipid bilayer membranes and the permeability properties of the pores studied. Triton X-100 solubilised porin samples showed large and reproducible increases in membrane conductivity composed of discreet single-channel events. The magnitude of the cation selectivity found for the porins was in the order OmpC greater than OmpF greater than NmpC = Lc; PhoE was anion selective. For the cation selective porins the cation/anion permeability ratios in a variety of solutes ranged from 6 to 35. Further information on the internal structure of the porins was obtained by examination of the single-channel conductance and this was used to interpret macroscopic observations and to estimate single-channel diameters. The same porins solubilised in SDS exhibited slight conductance increase with no observable single-channel activity. Use of on-line microcomputer techniques confirmed the ohmic current vs. voltage behaviour for all the single porin channels examined.

Ion selectivity of gram-negative bacterial porins

Twelve different porins from the gram-negative bacteria Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, and Yersinia pestis were reconstituted into lipid bilayer membranes. Most of the porins, except outer membrane protein P, formed large, water-filled, ion-permeable channels with a single-channel conductance between 1.5 and 6 nS in 1 M KCl. The ions used for probing the pore structure had the same relative mobilities while moving through the porin pore as they did while moving in free solution. Thus the single-channel conductances of the individual porins could be used to estimate the effective channel diameters of these porins, yielding values ranging from 1.0 to 2.0 nm. Zero-current potential measurements in the presence of salt gradients across lipid bilayer membranes containing individual porins gave results that were consistent with the conclusions drawn from the single-channel experiments. For all porins except protein P, the channels exhibited a greater cation selectivity for less mobile anions and a greater anion selectivity for less mobile cations, which again indicated that the ions were moving inside the pores in a fashion similar to their movement in the aqueous phase. Three porins, PhoE and NmpC of E. coli and protein P of P. aeruginosa, formed anion-selective pores. PhoE and NmpC were only weakly anion selective, and their selectivity was dependent on the mobility of the ions. In contrast, cations were unable to enter the selectivity filter of the protein P channel. This resulted in a high anion selectivity for all salts tested in this study. The other porins examined, including all of the known constitutive porins of the four gram-negative bacteria studied, were cation selective with a 3- to 40-fold preference for K+ ions over Cl- ions.

Evidence that the outer membrane protein gene nmpC of Escherichia coli K-12 lies within the defective qsr' prophage

Recombinants between phage lambda and the defective qsr' prophage of Escherichia coli K-12 were made in an nmpC (p+) mutant strain and in the nmpC+ parent. The outer membrane of strains lysogenic for recombinant qsr' phage derived from the nmpC (p+) strain contained a new protein identical in electrophoretic mobility to the NmpC porin and to the Lc porin encoded by phage PA-2. Lysogens of qsr' recombinants from the nmpC+ strain and lysogens of lambda p4, which carries the qsr' region, did not produce this protein. When observed by electron microscopy, the DNA acquired from the qsr' prophage showed homology with the region of the DNA molecule of phage PA-2 which contains the lc gene. Relative to that of the recombinant from the nmpC (p+) mutant, the DNA molecule of the recombinant from the nmpC+ parent contained an insertion near the lc gene. These results were supported by blot hybridization analysis of the E. coli chromosome with probes derived from the lc gene of phage PA-2. A sequence homologous to the lc gene was found at the nmpC locus, and the parental strains contained an insertion, tentatively identified as IS5B, located near the 3' end of the porin coding sequence. We conclude that the structural gene for the NmpC porin protein is located within the defective qsr' prophage at 12.5 min on the E. coli K-12 map and that this gene can be activated by loss of an insertion element.

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.

Bacteriophage T5 gene A2 protein alters the outer membrane of Escherichia coli

Evidence for changes in Escherichia coli envelope structure caused by the bacteriophage T5 gene A2 protein was obtained by the use of mutant bacteriophages, envelope fractionation procedures, electrophoretic analysis, and in vitro binding studies with purified gene A2 protein. The results suggested that the T5 gene A2 protein perturbs the host envelope as it functions to promote DNA transfer.

Comparison of sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles and antigenic relatedness among outer membrane proteins of 49 Brucella abortus strains

Outer membrane proteins were solubilized from 49 strains of Brucella abortus by sequential extraction of physically disrupted cells with N-lauroylsarcosinate and a dipolar ionic detergent (Verstreate et al., Infect. Immun. 35:979-989, 1982). The strains tested included standard agglutination test strain 1119, virulent strain 2308, and eight reference strains representing each of the biotypes; the remainder were isolates from cattle in North America with natural infections and included biotypes 1, 2, and 4. Three principal protein groups with apparent molecular weights of 88,000 to 94,000 (group 1), 35,000 to 40,000 (group 2, now established as porins [Douglas et al., Infect. Immun. 44:16-21, 1984]), and 25,000 to 30,000 (group 3) were observed in every strain. Some variability in banding patterns occurred among strains, but intrastrain variation was sufficient to preclude the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of outer membrane proteins for differentiating among strains of B. abortus. One antigen ([b]) was shared among the porin proteins, and three others ([c], ([d], and ([ e]) were shared among the group 3 proteins of all of the strains tested, indicating that these relationships are probably species wide. These results suggest that it may be possible to use outer membrane proteins from a representative strain of B. abortus in a vaccine for species-wide immunization.

Outer membrane protein NmpC of Escherichia coli: pore-forming properties in black lipid bilayers

The purified NmpC outer membrane protein from Escherichia coli, when incorporated into planar lipid bilayers, gave rise to channels with a single-channel conductance of 1.8 nS in 1 M KCl. This suggests that the NmpC protein is a porin.

Regulation of outer membrane protein synthesis in Escherichia coli K-12: deletion of ompC affects expression of the OmpF protein

A chromosomal deletion beginning at a Tn10 located ca. 8 kilobases upstream from the ompC structural gene and extending through the 2.6-kilobase HindIII fragment carrying the ompC was isolated. The 2.6-kilobase ompC fragment was cloned into lambda 540 to obtain phage lambda 540C1. When the deletion mutant was lysogenized with lambda 540C1, the resulting strain produced normal levels of OmpC protein, and expression of this protein was regulated by osmolarity, carbon source, and the lc gene of phage PA-2, indicating that the cloned fragment contained all of the information required for regulated expression of ompC. The strain carrying the deletion was partially constitutive for expression of OmpF protein, whereas the lambda 540C1 lysogen of this strain and other strains with mutations in ompC repressed OmpF synthesis under conditions which lead to high-level expression of OmpC protein. Strains which are diploid or triploid for ompC show strong inhibition of synthesis of OmpF protein. We conclude that a regulatory element located upstream from the ompC coding sequence inhibits translation of OmpF protein under conditions which favor OmpC expression. Since ompF is known to repress transcription of ompC, we propose that these two genes constitute a closed regulatory loop which acts to amplify regulatory signals which control expression of these proteins.

Penetration of moxalactam into its target proteins in Escherichia coli K-12: comparison of a highly moxalactam resistant mutant with its parent strain

An eschericia coli K-12 mutant highly resistant to moxalactam but only slightly resistant to other beta-lactam antibiotics was obtained by mutagen treatment. The affinity of moxalactam for its target penicillin-binding proteins was unchanged, as was the level of beta-lactamase activity. The penetration of [14C] moxalactam, however, was markedly reduced in the mutant. Electrophoretic analysis revealed alterations of the outer membrane proteins. A reduction in the amount of one of the pore-forming proteins (porins) was especially noteworthy. These data suggest that moxalactam resistance is the result of an alteration in the outer membrane structure.

Regulation of the OmpA outer membrane protein of Escherichia coli

The role of lipopolysaccharide in regulating the expression of the ompA outer membrane protein gene of Escherichia coli K-12 was studied by isolating mutants defective in the biosynthesis of lipopolysaccharide and by examining transcription of lacZ in strains carrying operon fusions in which lacZ is expressed from the ompA promoter. By selecting for simultaneous resistance to phages K3 and U3, we obtained mutants defective in rfaC (biosynthesis of core heptose) and in rfaP (phosphorylation of core heptose), and both of these mutant strains failed to express OmpA protein in the outer membrane. Expression of lacZ from the ompA or by foreign ompA alleles which are not expressed in E. coli K-12. Expression was increased in strains carrying rfaC and rfaP mutations. No precursor or degraded form of OmpA protein accumulated in cells which could not express the protein in the outer membrane. This lack of accumulation of precursor was observed even in the presence of phenethyl alcohol, which caused accumulation of OmpA precursor in wild-type cells. We present a model for the regulation of this gene which is consistent with these observations and which involves modulation of transcription coupled to translation of the protein.

Localization of phoE, the structural gene for outer membrane protein e in Escherichia coli K-12

To localize the structural gene for outer membrane protein e, mutants resistant to the protein e-specific phage TC45 were isolated and characterized. Three classes of TC45-resistant strains were found: (i) mutants in phoB, a regulatory gene for protein e, (ii) mutants with an altered lipopolysaccharide, and (iii) mutants unaltered in the regulation of the pho regulon and producing an apparently normal lipopolysaccharide. Mutations in the latter class of mutants are probably altered in the structural gene for protein e and are cotransducible with proA,B at min 6 on the chromosomal map. As class (iii) includes mutants with an electrophoretically altered protein e, in both an nmpA and an nmpB background, we conclude that the structural gene for protein e, designated as phoE, is localized at min 6 on the chromosomal map, the gene order being phoE proA argF.

Genetic and biochemical characterization of an Escherichia coli K-12 mutant with an altered outer membrane protein

The properties of an Escherichia coli K-12 mutant are described which seemingly produces a "new" major outer membrane protein with an apparent molecular weight of 40 000. This 40K protein was purified and its cyanogen bromide (CNBr) fragments were compared with those of several known major outer membrane proteins. A similarity was found between the CNBr fragments of the 40K protein and those of the OmpF protein (molecular weight 37 000). In addition, the 40K protein was found to be regulated exactly like the OmpF protein, and the mutation which causes the production of the 40K protein has been localized in (or very close to) the ompF gene. It is concluded that the 40K protein is a mutant form of the OmpF protein. The results provide additional evidence that the ompF gene at minute 21 is the structural gene for the OmpF protein.

Iron uptake in pseudorevertants of Escherichia coli K-12 mutants with multiple defects in the enterochelin system

Iron uptake in pseudorevertants of Escherichia coli K-12 strains which lack the ability to synthesize enterochelin, 2,3 dihydroxybenzoate, and the ferrienterochelin receptor protein was characterized. In four independent pseudorevertants, the suppressor mutations which permitted growth in iron-poor environments appeared to be located in omp B, the regulatory locus for the porin proteins. Unlike wild-type cells, the pseudorevertants were unable to utilize ferrienterochelin and could acquire iron from citrate without induction by prior growth in citrate. The energy requirements of the pseudorevertant system appeared to be identical to those of the enterochelin system. Evidence that loss of the porin proteins results in the secretion by the pseudorevertants of a molecule with siderophore activity is presented; this siderophore is able to remove iron from the non-biological iron chelators nitrilotriacetic acid and alpha, alpha'-dipyridyl but not fom the siderophores ferrichrome and enterochelin.

Specialized transducing bacteriophage lambda carrying the structural gene for a major outer membrane matrix protein of Escherichia coli K-12

A specialized transducing phage lambda carrying the structural gene for the OmpF protein, an outer membrane matrix protein, was isolated. The phage carries the 20.5--21-min region of the Escherichia coli K-12 chromosome and carries asnS, ompF, and aspC genes.

Precursor proteins are intermediates in vivo in the synthesis of two major outer membrane proteins, the OmpA and OmpF proteins, of Escherichia coli K12

The OmpA and OmpF proteins are major outer membrane proteins of Escherichia coli K12. Their precursors, the pro-OmpA and pro-OmpF proteins, have been detected in vivo in pulse-labelling experiments carried out with [35S]methionine at 25 degrees C. Wehn the pulse was at 37 degrees C, however, no precursors were detected. The pulse-labelled precursors were processed rapidly and quantitatively into mature protein at 25 degrees C. The apparent half-life of the pro-OmpF protein was estimated to be 30 s, and the pro-OmpA protein may be processed even faster. In short pulses (10 s) the precursors of both proteins were the predominant labelled species, indicating that at 25 degrees C processing does not start until chain elongation of the precursor is almost, if not entirely, complete. When French press lysates of cells pulse-labelled for 10 s were subjected to sucrose gradient centrifugation to separate the inner and outer membranes, both precursors comigrated with the inner membrane.

Regulatory mutations conferring constitutive synthesis of major outer membrane proteins (OmpC and OmpF) in Escherichia coli

An ompB strain of Escherichia coli K-12 lacking major outer membrane proteins OmpC and OmpF was used to isolate a pair of mutants that have restored the ability to synthesize either OmpC or OmpF protein. These mutants were found to produce the respective proteins constitutively under the several conditions where the synthesis in the wild-type strain was markedly repressed; namely, in the absence of the ompB gene function, under restrictive medium conditions, or upon lysogenization with phage PA-2. The mutations ompCp1 and ompFp9 responsible for such synthesis were shown to be located in the close vicinity of the corresponding structural genes, ompC and ompF. Moreover, the mutations affect the expression of these genes in a cis-dominant fashion. Taken together with other evidence, it was suggested that ompCp1 and ompFp9 represent regulatory site mutations occurring at the promoter regions of ompC and ompF respectively. Relevance of these findings to the genetic control of outer membrane protein synthesis is discussed.

Major heat-modifiable outer membrane protein in gram-negative bacteria: comparison with the ompA protein of Escherichia coli

The outer membranes of several strains of Escherichia coli, other enteric bacteria, and a variety of nonenteric gram-negative bacteria all contain a major heat-modifiable protein similar to the OmpA protein of E. coli K-12. The heat-modifiable proteins from these bacteria resemble the K-12 protein in molecular weight, in preferential release from the outer membrane by sodium dodecyl sulfate in the presence of Mg2+, and in characteristic cleavage by proteases to yield a smaller fragment which remains membrane bound. Antiserum directed against the K-12 protein precipitated the heat-modifiable protein from all strains of Enterobacteriaceae, and chemical comparison by isoelectric focusing, cyanogen bromide cleavage profiles, and proteolytic peptide analysis indicated that the proteins from the various enteric bacteria were nearly identical in primary structure. The heat-modifiable proteins from bacteria phylogenically distant from E. coli shared many of the properties of the E. coli protein but were chemically distinct. Thus, it appears that the structure (and, presumably, the function) of the heat-modifiable protein of gram-negative bacteria is strongly conserved during evolution.

Outer membrane protein e of Escherichia coli K-12 is co-regulated with alkaline phosphatase

Outer membrane protein e is induced in wild-type cells, just like alkaline phosphatase and some other periplasmic proteins, by growth under phosphatase limitation. nmpA and nmpB mutants, which synthesize protein e constitutively, are shown also to produce the periplasmic enzyme alkaline phosphatase constitutively. Alternatively, individual phoS, phoT, and phoR mutants as well as pit pst double mutants, all of which are known to produce alkaline phosphatase constitutively, were found to be constitutive for protein e. Also, the periplasmic space of most nmpA mutants and of all nmpB mutants grown in excess phosphate was found to contain, in addition to alkaline phosphatase, at least two new proteins, a phenomenon known for individual phoT and phoR mutants as well as for pit pst double mutants. The other nmpA mutants as well as phoS mutants lacked one of these extra periplasmic proteins, namely the phosphate-binding protein. From these data and from the known positions of the mentioned genes on the chromosomal map, it is concluded that nmpB mutants are identical to phoR mutants. Moreover, some nmpA mutants were shown to be identical to phoS mutants, whereas other nmpA mutants are likely to contain mutations in one of the genes phoS, phoT, or pst.

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.

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.

Correlation between the expression of an Escherichia coli cell surface protein and the ability of the protein to bind to lipopolysaccharide

The ompA gene of Escherichia coli codes for a major protein of the outer membrane. When this gene was moved between various unrelated strains (E. coli K-12 and two clinical isolates of E. coli) by transduction, the gene was expressed very poorly. Recombinants carrying "foreign" genes produced no OmpA protein which could be detected on polyacrylamide gels and became resistant to bacteriophage K3, which uses this protein as receptor. The recombinants were sensitive to host-range mutants of K3, indicating a very low level of OmpA protein was produced. When an E. coli K-12 recombinant carrying an unexpressed foreign ompA allele was subjected to two cycles of selection for an OmpA(+) phenotype, a mutant strain was obtained which was sensitive to K3 and which expressed nearly normal levels of OmpA protein in the outer membrane. This strain carried mutations in the foreign ompA gene, as indicated both by genetic mapping and the alteration of a peptide in the mutant OmpA protein. The ability of the OmpA protein to bind to lipopolysaccharide (LPS) showed similar strain specificity, and the mutant OmpA protein which was expressed in an unrelated host showed enhanced ability to bind LPS from its new host. Thus, cell surface expression of the ompA gene appears to depend upon the ability of the gene product to bind LPS, suggesting that an interaction between the protein and LPS plays an essential role in biosynthesis of this outer membrane protein.

Correlation between the expression of an Escherichia coli cell surface protein and the ability of the protein to bind to lipopolysaccharide

The ompA gene of Escherichia coli codes for a major protein of the outer membrane. When this gene was moved between various unrelated strains (E. coli K-12 and two clinical isolates of E. coli) by transduction, the gene was expressed very poorly. Recombinants carrying "foreign" genes produced no OmpA protein which could be detected on polyacrylamide gels and became resistant to bacteriophage K3, which uses this protein as receptor. The recombinants were sensitive to host-range mutants of K3, indicating a very low level of OmpA protein was produced. When an E. coli K-12 recombinant carrying an unexpressed foreign ompA allele was subjected to two cycles of selection for an OmpA(+) phenotype, a mutant strain was obtained which was sensitive to K3 and which expressed nearly normal levels of OmpA protein in the outer membrane. This strain carried mutations in the foreign ompA gene, as indicated both by genetic mapping and the alteration of a peptide in the mutant OmpA protein. The ability of the OmpA protein to bind to lipopolysaccharide (LPS) showed similar strain specificity, and the mutant OmpA protein which was expressed in an unrelated host showed enhanced ability to bind LPS from its new host. Thus, cell surface expression of the ompA gene appears to depend upon the ability of the gene product to bind LPS, suggesting that an interaction between the protein and LPS plays an essential role in biosynthesis of this outer membrane protein.

In vivo effects of local anesthetics on the production of major outer membrane proteins by Escherichia coli

Synthesis of a major outer membrane pore protein (the OmpF protein) by Escherichia coli K-12 was specifically and reversibly inhibited by low doses of procaine and other local anesthetics. The treated cells maintained the same total number of pores in their outer membrane by increased synthesis of the OmpC pore protein. Procaine also inhibited synthesis of the OmpF protein by Salmonella typhimurium and by E. coli B, although in the latter case, some OmpF protein was still detected in the outer membrane of treated cells. Experiments in which transcription was blocked by pretreatment with rifampicin indicated that procaine did not inhibit translation of the stable OmpF mRNA and that there was no pool of preformed OmpF and mRNA in cells grown in the presence of procaine. Procaine did not affect biosynthesis of the lipopolysaccharide core and did not inhibit the association of OmpF protein with the peptidoglycan. These results are discussed in terms of the known effects of procaine on membrane molecular packaging.

Comparison of outer membrane porin proteins produced by Escherichia coli and Salmonella typhimurium

The OmpC, OmpF, and Lc (NmpC) porin proteins of Escherichia coli K-12 have been shown to be similar to the OmpC (36K), OmpF (35K) and OmpD (34K) porin proteins of Salmnella typhimurium LT2 in terms of function, regulation of expression, and, in the case of OmpC and OmpF proteins, equivalence of the genetic loci determining their production. However, the corresponding pairs of proteins from these two species showed only limited similarity in peptide maps and no similarity in terms of migration on polyacrylamide gels.

Factors affecting the electrophoretic mobility of the major outer membrane proteins of Escherichia coli in polyacrylamide gels

The outer membrane proteins of Escherichia coli can be resolved by polyacrylamide gel electrophoresis in the presence of anionic detergents. Factors such as the choice of detergent and buffer system and the presence of urea in the separation gel are all shown to affect the charge and/or the configuration of the detergent-protein complexes and will affect the relative migration of these complexes to different extents. The procedures described in this paper may be of use in the determination of the relatedness of the proteins from the same or different strains. In addition, detailed examinations of the effects of these different parameters and the effect of changes in acrylamide concentrations may be useful in the detection of unusual characteristics which may indicate the presence of posttranslational modification.