Organization of proteins in the native and reformed outer membrane of Escherichia coli

Pore-forming activity of Coxiella burnetii outer membrane protein oligomer comprised of 29.5- and 31-kDa polypeptides. Inhibition of porin activity by monoclonal antibodies 4E8 and 4D6

Envelopes of large-cell variant Coxiella burnetii, the agent of Q fever, were the starting material for purification of an outer membrane protein (OMP) oligomer with aggregate molecular mass of approximately 2 x 10(4) kDa. The oligomer was resistant to trypsin and dissociation by SDS at 100 degrees C. Reducing agents dissociated the oligomer into monomers of 29.5 and 31 kDa, which migrated as a doublet during SDS-polyacrylamide gel electrophoresis. Both monomers were reactive in an immunoblot assay with monoclonal antibodies (mAbs) 4E8 and 4D6, which were previously selected for their reactivity with purified and SDS-denatured 29.5 kDa protein. Proteoliposomes were functional in an equilibrium assay at pH 7 and a swelling assay at pH 7 and 4.5. The pores in proteoliposomes allowed the passage of arabinose, glucose, and sucrose, but restricted stachyose. Polyclonal antibodies to C. burnetii cells and the mAbs were able to bind C. burnetii at pH 7 and 4.5. The uptake of 14C-glucose at pH 4.5 was inhibited by polyclonal antibodies and mAbs after binding to cells at pH 7. The mAbs did not inhibit 14C-glucose uptake at pH 4.5 after binding to cells at pH 4.5. Although the mAbs bind C. burnetii porin epitopes before and after acid activation, the mAbs bound under acidic conditions were unable to inhibit porin function. The inhibition of porin channel function by mAbs confirms the role of porin as a permeability barrier for the subsequent active transport of glucose by C. burnetii. In another study, we showed that the 29.5 kDa OMP antigen induced active immunity against virulent challenge. This information, combined with the recent confirmation that porins are important antigens in the induction of specific protective immune responses against infection by gram-negative bacteria, suggests that humoral immunity directed against C. burnetii porins might play an important role in immunity against Q fever (human infection) and coxiellosis (animal infection), global enzootic diseases.

The use of sarkosyl in generating soluble protein after bacterial expression

Actin, like many other proteins, is highly insoluble after expression in Escherichia coli. In order to understand the origin of insoluble aggregates, we asked whether morphological inclusions were always correlated with insolubility. The strain expressing actin was compared to one that expresses part of the myosin tail; the latter strain yields soluble protein after various cell lysis or disruption procedures. Morphological inclusions were observed in both strains, indicating there is no obligate relationship between solubility and inclusions. Studies presented here suggest that extreme insolubility results from coaggregation of the actin with bacterial outer membrane components upon bacterial lysis. The properties of the outer membrane have been exploited in the development of nondenaturing procedures that yield soluble actin. One procedure involves the disruption of coaggregates with sarkosyl detergent (N-laurylsarcosine); another prevents the formation of coaggregates by lysing in the presence of sarkosyl. These methods may be useful for other proteins that become insoluble after bacterial expression.

The porin protein of the outer membrane of Escherichia coli: reactivity in immunoblotting, antibody-binding by the native protein, and cross-reactivity with other enteric bacteria

The experimental conditions for antibody-binding by the 38.5 kD porin protein of an E. coli 055 strain in immunoblotting were investigated. A non-ionic detergent in the buffer which contained the primary antibody was required for antibody-binding by electroblots of the SDS-denatured protein. Immunoblotting, using antiserum absorbed with bacteria or the outer membrane (OM) of the E. coli 055 strain, showed results concordant with inaccessibility to antibodies of the 38.5 kD porin protein in its native configuration in the bacterial cells, but immunoreactivity when contained in the OM. OM from strains of different genera of the Enterobacteriaceae and antisera against these strains when used in immunoblot analyses showed that the E. coli 055 porin protein harboured antigenic determinants which are common to the various genera of the enteric bacilli. Cross-reactivity with non-enteric Gram-negative bacteria was not observed.

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.

Bdellovibrio bacteriovorus synthesizes an OmpF-like outer membrane protein during both axenic and intraperiplasmic growth

Outer membrane preparations of Bdellovibrio bacteriovorus grown intraperiplasmically on Escherichia coli containing OmpF were prepared by the Triton X-100 procedure of Schnaitman (J. Bacteriol. 108:545-552, 1971). They contained a protein that migrated to almost the same position as E. coli OmpF in sodium dodecyl sulfate-acrylamide gradient gel electrophoresis and to the same position as E. coli OmpF when urea was incorporated into the gel. The mobility of this protein increased relative to that of OmpC in urea-containing gels as does E. coli OmpF. However, the same protein was also produced during axenic growth and during intraperiplasmic growth on prey lacking OmpF. The peptide profile generated by partial proteolysis of this protein showed no homology to that produced from E. coli OmpF. We conclude that B. bacteriovorus synthesizes an OmpF-like protein. Previous claims that the bdellovibrio incorporates an intact E. coli OmpF are not consistent with these observations.

A high-molecular-mass cell wall protein released from Clostridium tyrobutyricum by heat treatment

Analysis of the cell wall of 4 strains of Clostridium tyrobutyricum reveals an unusually high protein content (35-40% dry weight). Brief heat treatment of whole cells of these stains causes release of two proteins, flagellin and a cell wall component of high molecular mass (110-125 kDa in the different strains). This component represents approx. 5% of the dry cell weight.

Influence of heat and sodium dodecyl sulfate on the endopeptidase I from Bacillus sphaericus 9602

Endopeptidase I from Bacillus sphaericus is a stable enzyme which retains its activity at 37 degrees C in the presence of sodium dodecyl sulfate. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed two forms of the enzyme: an active, fast-running form, for the enzyme preheated at 37 degrees C and a denatured, slow-running form, for the enzyme preheated at 100 degrees C. Such behavior is similar to that of the "heat-modifiable" outer membrane proteins from gram-negative bacteria. In the absence of sodium dodecyl sulfate, endopeptidase I aggregated in an enzymatically active dimer, with an apparent molecular weight of 90,000 daltons, which could be the native form of the enzyme.

Studies on the expression of outer membrane protein 2 in escherichia coli

The relative level of protein 2 expressed in the outer membrane of strains of Escherichia coli K-12 lysogenized with bacteriophage PA-2 was found to be influenced by both the growth temperature and lc+ gene dosage. An increase in either of these parameters was accompanied by an increase in the level of protein 2 up to an apparent saturation level. Any increase in the amount of protein 2 was accompanied by a concomittant decrease in the amount of OmpF and OmpC porins. This inverse relationship led to the maintenance of an approximately constant protein mass per unit of peptidoglycan. Our results are discussed in light of recent genetic studies on the regulation of the OmpF and OmpC porins and can be explained through the competition of these three matrix proteins for a common export or insertion site.

Interactions of cations with membrane fractions of smooth and rough strains of Salmonella typhimurium and other Gram-negative bacteria

Addition of cations (20 to 50 mM for Mg(2+) or Ca(2+) or 100 to 500 mM for Na(+)) to N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer during preparation of membranes from smooth and rough strains of Salmonella typhimurium LT2, Salmonella minnesota, and Escherichia coli O8 had two effects on the composition of the membranes isolated. First, in rough strains of chemotypes Ra to Re the "total membranes" (pellets from high-speed centrifugation) were deficient in the proteins of the outer membrane. The missing proteins were found to have been sedimented in a prior low-speed centrifugation in a fraction we call "cation-aggregated membranes." Since these membranes were enriched for lipopolysaccharide and for outer membrane proteins, deficient in succinic dehydrogenase, and contained primarily the dense peak after sucrose gradient centrifugation, it appears to be relatively pure outer membrane. About 10% of the membrane protein of smooth strains and up to 50% that of rough strains were cation-aggregated membranes, appearing to contain most of the outer membrane of rough strains. Thus, cation aggregation may be a useful means of preparation of outer membrane samples. The second effect was that with cation addition, several high-molecular-weight proteins not seen when membranes were prepared without cation addition were found in the total membranes of both smooth and rough strains after high-speed centrifugation. These proteins were bound by cations to the inner membranes, since they were soluble in Triton X-100 and separated into the less dense peak upon sucrose gradient centrifugation. They originated from the cytoplasm or the periplasm, since they corresponded to soluble proteins found in the supernatant after high-speed centrifugation and were depleted from this supernatant when preparation was done in the presence of cations.

Identification and preliminary characterization of Vibrio cholerae outer membrane proteins

Outer membrane proteins of Vibrio cholerae were purified by sucrose density centrifugation and Triton X-100 extraction at 10 mM Mg2+. The proteins were separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. V. cholerae outer membrane proteins presented a unique pattern when compared with the patterns of other gram-negative rods. There were 8 to 10 major bands (Mr 94,000 to 27,000), with most of the protein located in band 5 (Mr approximately 45,000), which thus appears to be the major structural protein of the outer membrane. Lipid and carbohydrate were associated with band 6.

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.

Characterization of the cell wall and cell wall proteins of Chromatium vinosum

Highly purified cell walls of Chromatium vinosum were isolated by differential centrifugation, with or without Triton X-100 extraction. The isolated material had a protein composition similar to that of cell walls obtained by sucrose density gradient centrifugation. Twenty-two proteins were reproducibly detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A 42-kilodalton protein was shown to account for 65% of the total cell wall protein. The majority of cell wall proteins were solubilized in sodium dodecyl sulfate at room temperature; however, they existed as high-molecular-weight complexes unless heated to 45 degrees C or above. The cell wall contained one heat-modifiable protein which migrated with an apparent molecular weight of 37,400 when solubilized at 70 degrees C or below, but which migrated with an apparent molecular weight of 52,500 if solubilized at 100 degrees C. The electrophoretic mobility of three proteins was modified by 2-mercaptoethanol. The majority of C. vinosum cell wall proteins had isoelectric points between pH 4.5 and 5.5, and the 42-kilodalton protein focused at pH 4.9. No proteins were detected which were analogous to the lipoprotein or peptidoglycan-associated proteins of the Enterobacteriaceae. Nearest-neighbor analysis with a reducible, cross-linking reagent indicated that three proteins, including the 42-kilodalton protein, associated with themselves. Most of the cell wall proteins were partially accessible to proteases in both intact cells and isolated cell walls. Protease treatment of the whole cell or isolated cell wall digested approximately an 11,000-molecular-weight portion of the 42-kilodalton protein.

Outer membrane of Pseudomonas aeruginosa: heat- 2-mercaptoethanol-modifiable proteins

A number of polyacrylamide gel systems and solubilization procedures were studied to define the number and nature of "major" polypeptide bands in the outer membrane of Pseudomonas aeruginosa. It was shown that five of the eight major outer membrane proteins were "heat modifiable" in that their mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was determined by the solubilization temperature. Four of these heat-modifiable proteins had characteristics similar to protein II of the Escherichia coli outer membrane. Addition of lipopolysaccharide subsequent to solubilization caused reversal of the heat modification. The other heat-modifiable protein, the porin protein F, was unusually stable to sodium dodecyl sulfate. Long periods of boiling in sodium dodecyl sulfate were required to cause conversion to the heat-modified form. This was demonstrated both with outer membrane-associated and purified lipopolysaccharide-depleted protein F. Furthermore, lipopolysaccharide treatment had no effect on the mobility of heat-modified protein F. Thus it is concluded that protein F represents a new class of heat-modifiable protein. It was further demonstrated that the electrophoretic mobility of protein F was modified by 2-mercaptoethanol and that the 2-mercaptoethanol and heat modification of mobility were independent of one another. The optimal conditions for the examination of the outer membrane proteins of P. aeruginosa by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis are discussed.

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.

Cyclic adenosine 3',5'-monophosphate regulation of the bacteriophage T6/colicin K receptor in Escherichia coli

Mutant strains of Escherichia coli unable to synthesize cyclic adenosine 3',5'-monophosphate (cAMP) or the cyclic adenosine monophosphate receptor protein (CRP) were more resistant than wild-type cells to infection by bacteriophage T6. This resistance was found to be associated with the decreased production of specific T6 receptor protein (also the colicin K receptor) located in the outer membrane protein fraction of these cells. Transcription of this particular outer membrane protein was regulated by the cAMP-CRP complex. A novel affinity technique coupled with sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used in these investigations.

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.

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.

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

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

Mutants (ompA) affecting a major outer membrane protein of Escherichia coli K12

Seventy independent mutants have been analyzed affecting a major protein, polypeptide II, of the outer cell envelope membrane from Escherichia coli K12. They were classified as nonsense mutants of the amber type (20%), mutants most likely of the missense type possessing the protein at normal concentrations (9%), and mutants either missing the protein or harboring it at much reduced concentrations for unknown reasons (71%). Forty of the mutants were analyzed genetically and all were found to map at or near ompA, the structural gene for protein II. Two-dimensional electrophoretic analyses of envelopes from such mutants revealed an unusual heterogeneity of the protein which on such patterns appeared as at least 12 well separated spots, and the majority of these is due to artifacts of the method but apparently specific for this protein. In no case was a polypeptide fragment found in envelopes from the nonsense mutants. The results are discussed regarding two different phages which use the protein as a receptor and concerning the biosynthetic incorporation of the protein into the outer membrane.

Porin activity in the osmotic shock fluid of Escherichia coli

Osmotic shock fluid of Escherichia coli exhibited pore-forming activity. This activity could be followed by an in vitro assay based on the conductivity increase for ions due to the presence of pores in black lipid membranes. The histogram (the distribution of conductivity increments in a single pore experiment) obtained with osmotic shock fluid from E. coli was identical to the histogram obtained by detergent-solubilized porin isolated from the outer membrane. The osmotic shock fluid from porin-negative mutants also exhibited pore activity, although the histogram and ion specificity were different from those of porin. Antibodies raised against detergent-solubilized porin were able to form precipitin lines by the Ouchterlony immunodiffusion technique when shock fluids, but not detergent-solubilized porin, were used. These antibodies prevented the formation of pores when shock fluids contained porin but not when shock fluids obtained from porin-negative mutants were used. Macroscopic membrane conductivity of shock fluids due to porin exhibited a concentration dependence, in contrast to detergent-solubilized porin. These results indicate that the hydrodynamic properties of periplasmic or "soluble" porin are different from those of the detergent-solubilized porin of the outer membrane. Periplasmic porin comprises about 0.7% of total protein in the osmotic shock fluid.

Membranes of Rhodopseudomonas sphaeroides. V. Identification of bacteriochlorophyll alpha-depleted cytoplasmic membrane in phototrophically grown cells

The separation of membrane fragments was investigated in extracts of phototropically grown Rhodopseudomonas sphaeroides to determine if the plasma membrane contains discrete regions. A highly purified fraction of bacteriochlorophyll alpha-deficient membrane fragments was isolated by differential centrifugation, chromatography on Sepharose 2B, reaggregation, and isopycnic sedimentation on sucrose gradients. Significant levels of b- and c-type cytochromes and succinate dehydrogenase were demonstrated in the isolated membrane fragments and their appearance in electron micrographs, their polypeptide profile in dodecyl sulfate-polyacrylamide gel electrophoresis, and overall chemical composition were essentially identical to a similar fraction isolated from aerobically grown cells. Their polypeptide profiles were distinct from those of the intracytoplasmic chromatophore and outer membranes, and on the basis of bacteriochlorophyll content the phototrophic fraction was contaminated with chromatophores by less than 9%. The membrane fragments contained no diaminopimelic acid or glucosamine. It is condluded that the membrane fragments isolated from phototrophically growing Rp. sphaeroides have arisen from photosynthetic pigment-depleted regions of the plasma membrane structurally and functionally differentiated from the intracytoplasmic chromatophore membrane. These regions represent conserved chemotrophic cytoplasmic membrane whose synthesis continues under photoheterotrophic conditions.

Structure of the cell wall of Bacillus species C.I.P. 76-111

An unusual type of bacterial cell wall was encountered in a Bacillus strain referred to as Bacillus sp. C.I.P. 76-111. The major constituent of this cell wall is a high-molecular-weight anionic protein non-covalently associated to a peptidoglycan-polysaccharide complex. The cell wall appeared as a multilayered structure when sections of whole cells or of isolated cell walls fixed with glutaraldehyde and postfixed with osmium tetroxide were examined by electron microscopy. The correlation between the observed morphological features and the biochemical data suggested that a thin central electron-dense layer identifiable with the peptidoglycan-polysaccharide complex is located between two similar thick layers of protein. Furthermore, negative staining of isolated cell walls revealed that the outer protein layer has a regular surface array of subunits with hexagonal symmetry. Several structural properties of the cell wall peptidoglycan were investigated and were found to resemble those of other bacilli. Further characterization of the autolytic system showed that an N-acetylmuramyl-L-alanine amidase and a glycosidase, presumably a N-acetylmuramidase, were associated with the peptidoglycan-polysaccharide complex. It was also established that this strain is devoid of membrane teichoic acid.

Outer membrane proteins of Escherichia coli. V. Evidence that protein 1 and bacteriophage-directed protein 2 are different polypeptides

Protein 1 from the outer membrane of Escherichia coli K-12 and protein 2 from a phage PA-2 lysogen of the same strain were isolated by differential sodium dodecyl sulfate extraction and purified by ion-exchange and gel filtration chromatography. Rabbit antisera were prepared against these proteins and showed no cross-reaction between proteins 1 and 2. The proteins have the same N-terminal amino acid but show small yet significant differences in amino acid composition. The proteins were cleaved with cyanogenbromide in solvents containing both formic acid and trifluoroacetic acid. By comparing the cleavage in these solvents, it was established that protein 1 yielded 5 cyanogen bromide peptides, and the sum of the molecular weights of these was equivalent to the molecular weight of the uncleaved protein. Protein 2 yielded 4 cyanogen bromide peptides, none of which was identical to those of protein 1, and the sum of these peptides was also equivalent to the apparent molecular weight of the uncleaved protein. Significant differences were also observed when tryptic peptides from the two proteins were compared. These results indicate that protein 1 and the phage-directed protein 2 are distinct, different, and apparently homogeneous proteins.

Outer membrane proteins of Escherichia coli. VI. Protein alteration in bacteriophage-resistant mutants

Protein 1 was shown to be the receptor for phage PA-2 by the observations that the purified protein inactivates the phage, mutants lacking the protein are resistant to the phage, and mutants selected for PA-2 resistance have altered protein. Protein 1 appears as two bands (1a and 1b) on high-resolution polyacrylamide gels. The most abundant classes of mutants (ParI and ParII) selected for PA-2 resistance were found to lack band 1b. The mutations responsible for the ParI and ParII phenotypes were mapped at a locus termed par, which is near nalA on the Escherichia coli chromosome. The cyanogen bromide peptides of proteins 1a and 1b are similar, suggesting that these bands represent modified forms of the same polypeptide. Strains carrying the tolF mutation produce only band 1b. When a par tolF double mutant was constructed, this strain produced only band 1a. These results suggest that genes at the par and tolF loci are involved in modification of protein 1, or regulation of such modification, and are not structural genes for protein 1.

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.

Cross-linking of the proteins in the outer membrane of Escherichia coli

1. The organization of the proteins in the outer membrane of Escherichia coli was examined by the use of cross-linking agents and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Treatment of protein A-peptidoglycan complexes with dithiobis(succinimidyl propionate) or glutaraldehyde produced the dimer, trimer, and higher oligomers of protein A. Both forms of this protein, proteins A1 and A2, produced similar cross-linking products. No cross-linking of protein A to the peptidoglycan was detected. 2. The proteins of the isolated outer membrane varied in their ease of cross-linking. The heat-modifiable protein, protein B, was readily cross-linked to give high molecular weight oligomers, while protein A formed mainly the dimer and trimer under the same conditions. The pronase resistant fragment, protein Bp, derived from protein B was not readily cross-linked. No linkage of protein A to protein B was detected. 3. Cross-linking of cell wall preparations, consisting of the outer membrane and peptidoglycan, showed that protein B and the free form of the lipoprotein, protein F, could be linked to the peptidoglycan. A dimer of protein F, and protein F linked to protein B, were detected. 4. These results suggest that specific protein-protein interactions occur in the outer membrane.

I. Structural proteins: effects of preparative conditions on the migration of protein in polyacrylamide gels

Coronavirus A59 possesses four size classes of structural proteins which have apparent molecular weights measured by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of 23,000 (GP23), 50,000 (VP50), 90,000 (GP90), and 180,000 (GP180). VP50 is the only structural protein which is completely unaffected by protease treatment of intact virions. This species is the most highly labeled by polar amino acids such as glutamic acid and arginine and it is probably associated with the viral nucleocapsid. GP90, GP180, and GP23 are membrane-associated proteins. However, after protease treatment of virions, only 20% of the GP23 molecule is digested, whereas all of the GP90 and GP180 are removed. GP90 and GP180 appear to comprise most of the prominent layer of characteristic projections on the external surface of the viral envelope. The major portion of GP23 is presumed to lie within the lipid envelope, protected from protease digestion. GP23 and the protease resistant portion, p^∗18, exhibit anomalous behavior on SDS-PAGE. After heating to 100° in SDS the electrophoretic mobility of these polypeptides is altered and several new forms of lower mobility are produced. β-Mercaptoethanol and dithiothreitol exaggerate the effects of heating.

Detergent-resistant phospholipase A of Escherichia coli K-12. Purification and properties

Detergent-resistant phospholipase A, which is tightly bound to the outer membranes of Escherichia coli K-12 cells, was purified approximately 2000-fold to near homogeneity by solubilization with sodium dodecylsulfate and butan-1-ol, acid precipitation, acetone fractionation and column chromatographies on Sephadex G-100 in the presence of sodium dodecylsulfate and on DEAE-cellulose in the presence of Triton X-100. The final preparation showed a single band in the sodium dodecylsulfate gel system. The enzyme hydrolyzes both the 1-acyl and 2-acyl chains of phosphatidylethanolamine or phosphatidylcholine. It also attacks 1-acyl and 2-acylglycerylphosphorylethanolamine. Thus, this enzyme shows not only phospholipase A1 and lysophospholipase L1 activities but also phospholipase A2 and lysophospholipase L2 activities. The enzyme lost its activity completely on incubation at 80 degrees C for 5 min at either pH 6.4 or pH 8.0. It was stable in 0.5% sodium dodecylsulfate at below 40 degrees C. The enzyme was inactivated on incubation for 5 min at 90 degrees C in 1% sodium dodecylsulfate/1% 2-mercaptoethanol/4 M urea. The native and inactivated enzymes showed different protein bands with RF values corresponding to Mr 21 000 and Mr 28 000 respectively, in a sodium dodecylsulfate gel system. Triton X-100 seemed to protect the enzyme from inactivation. The purified enzyme was fully active on phosphatidylethanolamine in the presence of 0.0002% or 0.05% Triton X-100. The enzyme requires Ca2+. From its properties this enzyme seems to be identical with the enzyme purified from crude extracts of Escherichia coli B by Scandella and Kornberg. However, it differs from the latter in its positional specificity and susceptibility to sodium dodecylsulfate. Possible explanation of the difference of positional specificity of the two preparations is also described.

Mutants of Escherichia coli "cryptic" for certain periplasmic enzymes: evidence for an alteration of the outer membrane

Mutants in which the expression of periplasmic enzymes by whole cells is reduced (termed "cryptic") are also found to show greatly reduced uptake of labeled adenosine 5'-monophosphate (5'-AMP), providing a rapid assay for crypticity. The crypticity of 3'- and 5'-nucleotidase has been examined as a function of substrate concentration. The Km for 3'- or 5'-AMP increases in the cryptic mutants when whole cells are used as the enzyme source. The Vmax is not altered. Electrophoretic analysis of protein prepared from cell envelopes showed that three cryptic mutants have a polypeptide absent from the outer membrane and a relatively high proportion of a polypeptide in the inner membrane. Analysis of the molar ratios of constituent sugars of the lipopolysaccharides showed no differences between three cryptic mutants and the parent strain. One cryptic mutant (3--41), however, has altered sensitivity to phage T4. By selection for phage resistance, derivatives of the cryptic mutants that are deoxycholate sensitive have been obtained. These mutants are no longer cryptic. We suggest that cryptic mutants have an altered outer membrane, with decreased permeability to 3'- and 5'-AMP, as a result of an altered polypeptide.

Mutational change of membrane architecture. Mutants of Escherichia coli K12 missing major proteins of the outer cell envelope membrane

Mutants of Escherichia coli have been analyzed which miss two of the major proteins of the outer cell envelope membrane. The two proteins I and II, normally are present at high concentrations (about 10(5) copies per cell). In such mutants, as compared with wild type, the phospholipid-to-protein ratio in the outer membrane has increased by a factor of 2.3 causing a considerable difference in density between wild type and mutant membranes. The concentrations of two other major components of the outer membrane, lipopolysaccharide and Braun's lipoprotein, did not change. The protein-deficient mutants do not exhibit gross functional defects in vitro. An increased sensitivity to EDTA and a slight such increase to dodecyl sulfate (but not to deoxycholate or Triton X-100) was observed, loss of so-called periplasmic enzymes was not found, and other differences to wild type are marginal. The mutants can grow with normal morphology. It is not possible, however, to prepare "ghosts" (particles of size and shape of the cell without murein, surrounded by a derivative of the outer membrane, and possessing the major proteins of this membrane) from them. This fact confirms our earlier suggestion that the proteins in question are required for the shape maintenance phenomenon in ghosts, and the mutants reject the speculation that these proteins are involved in the expression of the genetic information specifying cellular shape. Freeze-fracturing showed that in mutant cells, and in sharp contrast to wild type, the far predominant fracture plane is within the outer membrane. The concentration of the well known densely packed particles at the outer, concave leaflet of this fracture plane is greatly reduced. It was not possible, however, to clearly establish that one or the other protein is part of these particles because these ultrastructural differences were not apparent in mutants missing either one of the proteins only. The biochemical and ultrastructural data allow the conclusion that the loss of two major proteins and the concomitant increase of phospholipid concentration has changed the architecture of the outer membrane from a highly oriented structure, with a large fraction of protein-protein interaction, to one predominantly exhibiting planar lipid bilayer characteristics. E. coli thus can assemble rather different outer membranes, a fact excluding that outer membrane formation constitutes a highly ordered or strictly sequential assembly-line process.

Outer membrane of Escherichia coli K-12: isolation of mutants with altered protein 3A by using host range mutants of bacteriophage K3

A series of mutants has been isolated with alterations to protein 3A of the outer membrane. These mutations map at the previously described con locus as shown by cotransduction with pyrD. Most of them do not have detectable levels of protein 3A but are thought to have low levels of altered protein. These mutants have been detected by screening con mutants, isolated as resistant to bacteriophage K3, for their ability to plaque host range mutants of this bacteriophage. These host range phage mutants have activity spectra on the various con mutants that enable the bacterial mutants to be arranged in an order of increasing resistance to the host range phage mutants, from mutants sensitive to all host range phage to those sensitive to only one class. Likewise, the phage can be arragned in an order of increasing ability to plaque on the con mutants. Some of the mutants resemble the previously described con mutants in being tolerant to colicins K and L, and others resemble them in being highly defective as recipients with the F factor. These properties vary independently, suggesting that protein 3A can be modified to independently affect the three properties of bacteriophage receptor function, involvement in colicin sensitivity, and involvement in conjugation.

Outer membrane of Escherichia coli K-12: differentiation of proteins 3A and 3B on acrylamide gels and further characterization of con (tolG) mutants

Two classes of mutants, con and tolG, that appeared to be very similar in a number of respects have been shown to be identical and cotransducible with pyrD. By diethylaminoethyl-cellulose chromatography of the outer membranes, we have shown that the mutants are missing only protein 3A and retain protein 3B. Using con mutants, we were thus able to identify protein 3B on the pH 7.2 gel system of Maizel where it runs separately from protein 3A if unheated samples are used. tolG mutants were shown to be identical to con mutants in being conjugation defective with most F-like plasmid donors but not with I-like plasmid donors, and in their resistance pattern to bacteriophages and colicins. During the course of this study, it was observed that the bacteriocin produced by Serratia marcescenc JF246 was identical in its activity spectrum to colicin L-398 and is now considered to be a colicin of type L.

Membrane protein biosynthesis in bacteriophage BF23-infected Escherichia coli

When Escherichia coli is infected with bacteriophage BF23, two new proteins with molecular weights greater than 10,000, as indicated by polyacrylamide gel electrophoresis, are found associated with the cells' membranes. One of these, found associated with both the inner and outer membrane, has a molecular weight of about 55,000 and is regulated by the A1 gene of this phage, a gene found on the spontaneously injected 8% piece of BF23 DNA, DNA that codes for the synthesis of proteins necessary for the injection of the whole phage genome. The other protein, often undetected in whole membrane preparations, is found exclusively associated with the inner membrane. Evidence indicates that this protein is also regulated by the initially injected 8% piece of the DNA.

Characterization of group B colicin-resistant mutants of Escherichia coli K-12: colicin resistance and the role of enterochelin

Nine classes of group B colicin-resistant mutants were examined to study the role of enterochelin in colicin resistance. Four of the mutants studied (cbt, exbC, exbB, and tonB) hypersecreted enterochelin. Enterochelin hypersecretion was apparently responsible for resistance of the exbC mutant to colicins G and H and for resistance of the exbB mutant to colicins G, H, Ia, Ib, S1, and V. All four mutants scored as colicin B tolerant, even in the absence of enterochelin synthesis. The mutants produced substantially increased amounts of two high-molecular-weight outer membrane polypeptides when grown under limiting iron conditions. The presence of these polypeptides was correlated with increased colicin B-neutralizing activity in the outer membrane preparations.

Iron uptake in colicin B-resistant mutants of Escherichia coli K-12

Four classes of colicin B-resistant mutants of Escherichia coli K-12 were examined for defects in iron uptake. All four mutant classes (cbt, exbC, exbB, and tonB) were defective in the uptake of ferri-ennterochelin. The tonB mutant was also defective in citrate-, ferrichrome-, and rhodoturulic acid-mediated iron uptake. The defects in iron transport were reflected in increased sensitivity to iron chelators and to chromium and aluminium salts, and in hypersecretion of enterochelin. One of the mutants (cbt) was apparently defective in outer membrane ferri-enterochelin receptor activity. aroE derivatives (unable to synthesize enterochelin) of the four mutant classes and the parent strain produced increased amounts of two outer membranes polypeptides when grown under iron stress. These polypeptides are implicated in ferri-enterochelin receptor activity.

The major proteins of the Escherichia coli outer cell-envelope membrane. Heterogeneity of protein I

One of the major proteins of the Escherichia coli outer cell envelope membrane, protein I, can be separated electrophoretically into protein components Ia and Ib. Strain differences exist regarding presence or absence of component Ib and this component can selectively be lost by mutation to resistance against a phage. Both components Ia and Ib are further heterogeneous isoelectrically, and both together may contain at lease six separable isoelectric species. As judged by analysis of their cyanogen bromide fragments, Ia and Ib are almost identical concerning their primary structure; the difference (charge only or size and charge) was located in a part of the protein that does not correspond to the C-terminal or N-terminal regions. Components Ia and Ib thus represent essentially the same polypeptide and they may arise by a modification process in vitro or the existence of two almost identical genes.