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PubMed1997

Role of the colicin A lysis protein in the expression of the colicin A operon.

The involvement of the cal gene, which encodes the colicin A lysis protein, in the expression of the colicin A operon is demonstrated. Colicin A synthesis by Escherichia coli was studied at various temperatures in cells containing either the wild-type colicin A operon or the colicin A operon with the cal gene deleted. The amount of colicin A produced was lower in cells containing the colicin A operon devoid of the cal gene than in wild-type cells. In cells treated with the antibiotic globomycin, the synthesis of colicin A was blocked in null cal mutants at all temperatures. It was blocked only at low temperature in cells containing the wild-type colicin A operon, but not in cells subjected to heat shock or azide treatment. The cal gene product may be an activator of colicin A expression and of its own expression. An unidentified product, possibly a heat-shock protein, may also be involved and could complement the cal gene product in some situations.

Bacterial Proteins↗
PubMed1979

Mechanism of export of colicin E1 and colicin E3.

The mechanism of export of colicins E1 and E3 was examined. Neither colicin E1, colicin E3, Nor colicin E3 immunity protein appears to be synthesized as a precursor protein with an amino-terminal extension. Instead, the colicins, as well as the colicin E3 immunity protein, appear to leave the cells where they are made, long after their synthesis, by a nonspecific mechanism which results in increased permeability of the producing cells. Induction of ColE3-containing cells with mitomycin C leads to actual lysis of those cells, as some time after synthesis of the colicin E3 and its immunity protein has been completed. Induction of ColE1-containing cells results in increased permeability of the cells, but not in actual lysis, and most of the colicin E1 produced never leaves the producing cells. Intracellular proteins such as elongation factor G can be found outside of colicinogenic cells after mitomycin C induction, along with the colicin. Until substantial increases in permeability occur, most of the colicin remains cell associated, in the soluble cytosol, rather than in a membrane-associated form.

Bacterial Proteins↗
PubMed1987

Nucleotide sequence of the colicin B activity gene cba: consensus pentapeptide among TonB-dependent colicins and receptors.

Colicin B formed by Escherichia coli kills sensitive bacteria by dissipating the membrane potential through channel formation. The nucleotide sequence of the structural gene (cba) which encodes colicin B and of the upstream region was determined. A polypeptide consisting of 511 amino acids was deduced from the open reading frame. The active colicin had a molecular weight of 54,742. The carboxy-terminal amino acid sequence showed striking homology to the corresponding channel-forming region of colicin A. Of 216 amino acids, 57% were identical and an additional 19% were homologous. In this part 66% of the nucleotides were identical in the colicin A and B genes. This region contained a sequence of 48 hydrophobic amino acids. Sequence homology to the other channel-forming colicins, E1 and I, was less pronounced. A homologous pentapeptide was detected in colicins B, M, and I whose uptake required TonB protein function. The same consensus sequence was found in all outer membrane proteins involved in the TonB-dependent uptake of iron siderophores and of vitamin B12. Upstream of cba a sequence comprising 294 nucleotides was identical to the sequence upstream of the structural gene of colicin E1, with the exception of 43 single-nucleotide replacements, additions, or deletions. Apparently, the region upstream of colicins B and E1 and the channel-forming sequences of colicins A and B have a common origin.

Amino Acid Sequence↗
PubMed1966

Interaction of colicins with bacterial cells. I. Studies with radioactive colicins.

Maeda, Akio (Department of Genetics, University of Wisconsin, Madison), and Masayasu Nomura. Interaction of colicins with bacterial cells. I. Studies with radioactive colicins. J. Bacteriol. 91:685-694. 1966.-By use of a preparation of radioactive colicin E2, the following conclusions, which had been obtained previously from indirect experiments, were tested directly: (i) colicin stays at the receptor site on the cell and acts from there; (ii) colicins E2 and E3 share the same receptor, although their mode of action is entirely different; (iii) colicinogenic cells adsorb homologous colicin, although they are resistant to that colicin. Our experimental results confirmed the above conclusions. When sensitive cells of Escherichia coli K-12 pretreated with radioactive E2 were disrupted with a French pressure cell, and fractionated by differential centrifugation, it was found that most of the radioactivity stayed with the cell envelope fraction. Trypsin removed a major part of radioactivity from cells pretreated with radioactive E2, as was expected from the previous experiments on trypsin reversal of colicin action. Furthermore, it was shown that the trypsin treatment causes a recovery of the capacity of E2-pretreated cells to adsorb further colicin E2. When cells were first treated with various amounts of nonradioactive E3, and then treated with radioactive E2, the amount of radioactive E2 adsorbed was found to be inversely related to the amount of nonradioactive E3 adsorbed first. It was also shown that E2-colicinogenic cells adsorb radioactive E2, and yet are resistant to this colicin.

Adsorption↗
PubMed2000

The newly characterized colicin Y provides evidence of positive selection in pore-former colicin diversification.

Two evolutionary mechanisms have been proposed in the process of protein diversification of the large family of antimicrobial toxins of Escherichia coli, known as the colicins. Data from previous studies suggest that the relatively rare nuclease colicins appear to diversify primarily through the action of positive selection, whilst the more abundant pore-former colicins appear to diversify through the action of recombination. The complete DNA sequence of the newly characterized colicin plasmid, pCol-Let, isolated from a Yanomama Indian of South America, is presented here. This plasmid encodes a newly identified pore-former colicin, colicin Y. DNA and protein sequence comparisons of the colicin Y gene cluster and the encoded proteins with those of published pore-former colicins provide the first evidence that positive selection may also act to increase pore-former colicin diversity.

Colicins↗
PubMed2002

Colicins produced by the Escherichia fergusonii strains closely resemble colicins encoded by Escherichia coli.

Plasmid DNA of six Escherichia fergusonii colicinogenic strains (three producers of colicin E1, two of Ib and one of Ia) was isolated and the colicin-encoding regions of the corresponding Col plasmids were sequenced. Two new variants of colicin E1, one of colicin Ib, and one of colicin Ia were identified as well as new variants of the colicin E1 and colicin Ib immunity proteins and the colicin E1 lysis polypeptide. The recombinant Escherichia coli producer harboring pColE1 from E. fergusonii strain EF36 (pColE1-EF36) was found to be only partially immune to E1 colicins produced by two other E. fergusonii strains suggesting that pColE1-EF36 may represent an ancestor ColE1 plasmid.

Colicins↗
PubMed1970

Colicin-tolerant mutants of Escherichia coli: resistance of membranes to colicin E1.

Colicin E1 blocks proline accumulation by membrane vesicles prepared from wild-type sensitive Escherichia coli. Two classes of mutant cells are unaffected by colicin. Vesicles from colicin-resistant strains are sensitive to colicin E1, whereas vesicles from colicin-tolerant strains are unaffected by colicin El. These results suggest that the colicin E1 receptor is on the cell membrane and that colicin-tolerant strains have altered membranes while colicin-resistant strains have altered cell walls.

Biological Transport↗
PubMed1972

Specific inhibition of cell division by colicin E 2 without degradation of deoxyribonucleic acid in a new colicin sensitivity mutant of Escherichia coli.

A new class of colicin sensitivity mutants of Escherichia coli was isolated whose cell division was specifically inhibited by colicin E(2) without detectable degradation of deoxyribonucleic acid (DNA) at 30 C. The mutant could not form colonies in the presence of colicin E(2) but recovered colony-forming ability by trypsin treatment even after prolonged incubation with the colicin. Addition of colicin E(2) to the exponentially growing mutant inhibited cell division completely but did not induce degradation of DNA into cold acid-soluble materials nor any breakage of DNA strands. Synthesis of DNA in the mutant was not inhibited, and long filamentous cells with multiple nuclear bodies were formed by the action of colicin E(2). Degradation of ribosomal ribonucleic acid and development of prophage lambda, both of which were induced by colicin E(2) in the sensitive cells, did not occur in the mutant. At the elevated temperature, however, the mutant was found to undergo colicin-induced degradation of DNA. No differences in ultraviolet light nor drug sensitivities were observed in the mutant compared to the parent E. coli. The data suggested that colicin E(2) had a specific inhibitory effect on cell division of E. coli that was not a consequence of DNA degradation.

Bacteriological Techniques↗
PubMed1980

Outer membrane-dependent transport systems in Escherichia coli: effect of repression or cessation of colicin receptor synthesis on colicin receptor activities.

Proteins in the outer membrane of gram-negative bacteria serve as general porins or as receptors for specific nutrient transport systems. Many of these proteins are also used as receptors initiating the processes of colicin or phage binding and uptake. The functional activities of several outer membrane proteins in Escherichia coli K-12 were followed after cessation or repression of their synthesis. Cessation of receptor synthesis was accomplished with a thermolabile suppressor activity acting on amber mutations in btuB (encoding the receptor for vitamin B(12), the E colicins, and phage BF23) and in fepA (encoding the receptor for ferric enterochelin and colicins B and D). After cessation of receptor synthesis, cells rapidly became insensitive to the colicins using that receptor. Treatment with spectinomycin or rifampin blocked appearance of insensitive cells and even increased susceptibility to colicin E1. Insensitivity to phage BF23 appeared only after a lag of about one division time, and the receptors remained functional for B(12) uptake throughout. Therefore, possession of receptor is insufficient for colicin sensitivity, and some interaction of receptor with subsequent uptake components is indicated. Another example of physiological alteration of colicin sensitivity is the protection against many of the tonB-dependent colicins afforded by provision of iron-supplying siderophores. The rate of acquisition of this nonspecific protection was found to be consistent with the repression of receptor synthesis, rather than through direct and immediate effects on the tonB product or other components of colicin uptake or action.

Colicins↗
PubMed1982

Exchange of colicin receptor capacity between strains of Escherichia coli sensitive or resistant to colicin K-K235.

Phage and colicin-resistant mutants were derived from Escherichia coli K-12P678. Two classes of phage T6 and colicin K-resistant mutants (genotype tsx) were isolated. Tsx-2 mutants, which demonstrated mucoid growth and increased sensitivities to many antibiotics, became sensitive to colicin K when pretreated with ethylenediaminetetraacetate (EDTA), whereas Tsx-1 mutants did not. Reassociation of EDTA-released material partially restored resistance to colicin K for Tsx-2 mutants. When EDTA-released material from strain P678 was associated with either class of K-resistant mutant, an increase in colicin K sensitivity resulted. Observations suggest that colicin K can act on its target site once it penetrates the cell surface. In addition, results suggest that functional colicin K receptors can be transferred from sensitive to resistant strains, thus conferring colicin sensitivity.

Cell Membrane↗
PubMed1958

Colicine K. III. The immunological properties of a substance having colicine K activity.

By immunological means it has been shown that colicine K is associated with the O antigen of the colicinogenic bacillus E. coli K(235) L(+)OC(+). The colicine K-O antigen complex elicits the formation of at least two types of antibodies, one a precipitin, the other a colicine-neutralizing antibody. The first precipitates colicine K without neutralizing it, the second neutralizes the colicine without precipitating it. Unlike the purified colicine K complex, the colicine protein component of the O antigen is precipitable by the neutralizing antibody. There is no demonstrable serological relationship between colicine K and phage T(6). These two agents must be considered to be separate and distinct entities.

Anti-Bacterial Agents↗
PubMed1994

Colicin 24, a new plasmid-borne colicin from a uropathogenic strain of Escherichia coli.

A new colicin, as defined by cross-immunity tests against the colicin reference set, has been identified from a uropathogenic Escherichia coli isolate (strain 2424), collected from a pyelonephritis patient at Christchurch Hospital. This toxin, colicin 24, is active against E. coli and Salmonella typhimurium, and the genes involved in colicin 24 production, transport, and immunity were found to reside on a 43.54-kb conjugative plasmid, p24-2. Mutagenesis using mini-Tn10 has identified two consecutive EcoRI fragments on p24-2 that contain all the colicin 24 determinants. A 25.14-kb BamHI-HindIII fragment containing this region was cloned from a mutant with a normal colicin phenotype into pBR322 to form the recombinant plasmid pGOB34. Subcloning of pGOB34 has resulted in an 8.7-kb fragment containing all the colicin 24 determinants being cloned into pUC18 to form pGOB342.

Bacteriophage lambda↗
PubMed1987

Gating processes of channels induced by colicin A, its C-terminal fragment and colicin E1 in planar lipid bilayers.

The dependence on pH and membrane potential of the pore formed by colicin A and its C-terminal 20 kDa fragment has been measured using planar lipid bilayers. The single channel conductance of the pore formed by both colicin A and the fragment increases with pH with an apparent pK of 6.0. At pH 5.0 the gating by membrane potential of the channels formed by either colicin A or its fragment is identical. At the same pH, quite similar pore properties were found when using the related bacteriocin, colicin E1. In agreement with previous studies, these data indicate that the protein structure containing the lumen of the pore resides in the 20 kDa C-terminal part of the colicin A and favours the recently proposed model, based on protein sequence analysis, which proposes that colicin A, E1 and IB C-terminal domains are folded in the same three-dimensional structure. However, it is also shown that colicin A and not its C-terminal fragment undergoes a pH dependent transition between an "acidic" and a "basic" form of the pore with an apparent pK of 5.3. The two forms of the pore differ by their gating charge but not by the channel size. These results suggest that there is a pH dependent association between the C-terminal domain carrying the lumen of the pore and another domain of the molecule which affect the pore sensitivity to membrane potential.

Cell Membrane↗
PubMed2004

Gating movements of colicin A and colicin Ia are different.

Both colicin A and colicin Ia belong to a subfamily of the bacterial colicins that act by forming a voltage-dependent channel in the inner membrane of target bacteria. Both colicin A and Ia open at positive and close at negative potential, but only colicin A exhibits distinctly biphasic turnoff kinetics, implying the existence of two open states. Previous work has shown that Colicin Ia gating is associated with the translocation of a region representing 4 of its alpha helices across the membrane. Also, if its C-terminal, channel-forming domain is detached from the other domains, its N-terminal alpha helix can now also cross the membrane, causing the conductance to drop by a factor of about 6. Colicin A gating also involves the translocation of an internal domain, but we find that its translocated domain is somewhat smaller than that of Ia. Furthermore, while its isolated C-terminal domain can also undergo a transition to a smaller conductance, the conductance change is only about 15%, and the transition does not involve the translocation of the N-terminal alpha helix. Trapping the N-terminus on the cis side prevents neither this small conductance transition nor the biphasic turn-off. So, while the gating of both channels involves large, currently inexplicable conformational changes, these motions are qualitatively different in the two proteins, which may be a reflection of the dissimilar kinetics of closing.

Amino Acid Sequence↗
PubMed2002

Colicin crystal structures: pathways and mechanisms for colicin insertion into membranes.

The X-ray structures of the channel-forming colicins Ia and N, and endoribonucleolytic colicin E3, as well as of the channel domains of colicins A and E1, and spectroscopic and calorimetric data for intact colicin E1, are discussed in the context of the mechanisms and pathways by which colicins are imported into cells. The extensive helical coiled-coil in the R domain and internal hydrophobic hairpin in the C domain are important features relevant to colicin import and channel formation. The concept of outer membrane translocation mediated by two receptors, one mainly used for initial binding and second for translocation, such as BtuB and TolC, respectively, is discussed. Helix elongation and conformational flexibility are prerequisites for import of soluble toxin-like proteins into membranes. Helix elongation contradicts suggestions that the colicin import involves a molten globule intermediate. The nature of the open-channel structure is discussed.

Bacterial Outer Membrane Proteins↗
PubMed1987

Colicin Js of Shigella sonnei: classification of type colicin "7".

Colicinotype 7 of Shigella sonnei, introduced by Abbott and Graham, is one of those most frequently found in epidemiological screenings. It is represented by the production of a single colicin (acidic protein of m. w. 46 kD) endowed with some striking features. It is unstable at pH 8.0 and at the temperature of 70 degrees C. Its inhibitive activity is specific for the species Shigella sonnei, most strains of which seem to be sensitive. It is the only colicin known so far inactive towards Escherichia coli, including the indicator strains of broad-spectrum sensitivity, such as K12 Row. It shows no cross-resistance with any other colicin type. Its adsorption on sensitive bacteria and inhibitive effect on them proceed extremely quickly. As indicated by indirect fluorimetry, its mode of action is extremely quickly. As indicated by indirect fluorimetry, its mode of action is probably different from those known for other colicins: it does not concern the plasma membrane of sensitive bacteria under aerobiosis, but it interferes with it under anaerobic conditions. These data show clearly that it is a unique colicin type. It is proposed to include it into the current system of classified colicins as "colicin Js".

Bacterial Proteins↗
PubMed1996

The crystal structure of the immunity protein of colicin E7 suggests a possible colicin-interacting surface.

The immunity protein of colicin E7 (ImmE7) can bind specifically to the DNase-type colicin E7 and inhibit its bactericidal activity. Here we report the 1.8-angstrom crystal structure of the ImmE7 protein. This is the first x-ray structure determined in the superfamily of colicin immunity proteins. The ImmE7 protein consists of four antiparallel alpha-helices, folded in a topology similar to the architecture of a four-helix bundle structure. A region rich in acidic residues is identified. This negatively charged area has the greatest variability within the family of DNase-type immunity proteins; thus, it seems likely that this area is involved in specific binding to colicin. Based on structural, genetic, and kinetic data, we suggest that all the DNase-type immunity proteins, as well as colicins, share a "homologous-structural framework" and that specific interaction between a colicin and its cognate immunity protein relies upon how well these two proteins' charged residues match on the interaction surface, thus leading to specific immunity of the colicin.

Amino Acid Sequence↗