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D Baty

Publications and source records attributed to D Baty.

At least 55 records · Page 3Linked to original sources
PubMed1991

Construction, expression and release of hybrid colicins.

Colicins A and E1 are two pore-forming colicins sharing homology in their C-terminal domains but not in their N-terminal or central domains. Using site-directed mutagenesis, restriction sites were inserted at the proper locations to allow recombination of these domains. Six different constructs were obtained. All these proteins were expressed in Escherichia coli and properly recognized by monoclonal antibodies directed against epitopes located in different domains of colicin A. Out of the six hybrids, only two were released to the extracellular medium. Immunocytolocalization indicated that some of the hybrids aggregated within the cytoplasm. With some hybrids, the defect in release was related to a defect in synthesis of the lysis protein that normally promotes release.

Antibodies, Monoclonal↗
PubMed1991

Individual domains of colicins confer specificity in colicin uptake, in pore-properties and in immunity requirement.

Six different hybrid colicins were constructed by recombining various domains of the two pore-forming colicins A and E1. These hybrid colicins were purified and their properties were studied. All of them were active against sensitive cells, although to varying degrees. From the results, one can conclude that: (1) the binding site of OmpF is located in the N-terminal domain of colicin A; (2) the OmpF, TolB and TolR dependence for translocation is also located in this domain; (3) the TolC dependence for colicin E1 is located in the N-terminal domain of colicin E1; (4) the 183 N-terminal amino acid residues of colicin E1 are sufficient to promote E1AA uptake and thus probably colicin E1 uptake; (5) there is an interaction between the central domain and C-terminal domain of colicin A; (6) the individual functioning of different domains in various hybrids suggests that domain interactions can be reconstituted in hybrids that are fully active, whereas in others that are much less active, non-proper domain interactions may interfere with translocation; (7) there is a specific recognition of the C-terminal domains of colicin A and colicin E1 by their respective immunity proteins.

Bacterial Outer Membrane Proteins↗
PubMed1991

Characterization of endoglucanase A from Clostridium cellulolyticum.

A construction was carried out to obtain a high level of expression in Escherichia coli of the gene celCCA, coding for the endoglucanase A from Clostridium cellulolyticum (EGCCA). The enzyme was purified in two forms with different molecular weights, 51,000 and 44,000. The smaller protein was probably the result of proteolysis, although great care was taken to prevent this process from occurring. Evidence was found for the loss of the conserved reiterated domains which are characteristic of C. thermocellum and C. cellulolyticum cellulases. The two forms were extensively studied, and it was demonstrated that although they had the same pH and temperature optima, they differed in their catalytic properties. The truncated protein gave the more efficient catalytic parameters on carboxymethyl cellulose and showed improved endoglucanase characteristics, whereas the intact enzyme showed truer cellulase characteristics. The possible role of clostridial reiterated domains in the hydrolytic activity toward crystalline cellulose is discussed.

Amino Acid Sequence↗
PubMed1990

A 136-amino-acid-residue COOH-terminal fragment of colicin A is endowed with ionophoric activity.

DNA regions encoding the various domains of a protein can be expressed as separate entities by inserting at appropriate sites a 'STOP-Shine-Dalgarno-sequence-ATG' cassette encoding a termination codon, a Shine-Dalgano sequence and an initiation codon within the structural gene. This technique has been used to obtain a 137-amino-acid-residue pore-forming protein designated DA70C comprising the final 136-amino-acid-residue COOH-terminal of colicin A preceded by an NH2-terminal methionine. Da70C was correctly expressed but poorly released to the extracellular medium. Its purification involved, as a final step, a partition in Triton X-114 thus demonstrating that hydrophobic regions are exposed in this protein. The ability of DA70C to form ion channels in planar lipid bilayers was investigated and pore properties were analyzed. The results indicate that helices 1-3 of the 204-amino-acid-residue colicin pore-forming domain (containing 10 alpha-helices) are not involved in ion conduction through the channel. However, they are important in maintaining the stability of the soluble state of the COOH-terminal domain.

Amino Acid Sequence↗
PubMed1989

Synthesis and sequence-specific proteolysis of a hybrid protein (colicin A::growth hormone releasing factor) produced in Escherichia coli.

DNA constructs coding for human growth hormone (hGH)-releasing factor (hGRF) preceded by the specific recognition sequence for the activated blood coagulation factor X (FXa), fused in frame to the N-terminal 172-amino acid residues of colicin A, have been expressed in Escherichia coli. The construct was placed under the control of the inducible caa promoter in an operon containing a downstream gene coding for the cell lysis protein, Cal. Induction resulted in excretion of only the processed colicin A fragment. Replacement of Cal by the terminator from phage fd resulted in high expression of the hybrid protein, which was recovered as cytoplasmic aggregates. Enzymatic cleavage of the purified and renatured hybrid protein using FXa allowed the recovery of authentic hGRF.

Base Sequence↗
PubMed1989

Isolation and molecular and functional properties of the amino-terminal domain of colicin A.

A plasmid was constructed which allowed easy and efficient production and purification of the NH2-terminal domain of colicin A. In only three steps, an homogenous 18-kDa polypeptide was obtained. The NH2- and COOH-terminal sequences of the protein were determined and showed that it corresponded to the NH2-terminal 171 amino acid residues of the 63-kDa colicin A. Although colicin A is a highly asymmetric protein, hydrodynamic studies indicated that the NH2-terminal domain (designated AT) has a globular structure. This fragment is not the receptor-binding domain of colicin A but is required for the transfer of colicin A across the outer membrane of sensitive cells. However, it has a low affinity for phospholipid films and this affinity is not pH-dependent, in contrast to that of colicin A.

Amino Acid Sequence↗
PubMed1989

Interactions of colicin A domains with phospholipid monolayers and liposomes: relevance to the mechanism of action.

The colicin A polypeptide chain (592 amino acid residues) contains three domains which are linearly organized and participate in the sequential steps involved in colicin action. We have compared the penetrating ability in phospholipid monolayers and the ability to promote vesicle fusion at acidic pH of colicin A and of protein derivatives containing various combinations of its domains. The NH2-terminal domain (171 amino acid residues), required for translocation across the outer membrane, has little affinity for dilauroylphosphatidylglycerol (DLPG) monolayers at all pHs tested. The central domain has a pH-dependent affinity, although lower than that of the entire colicin A. The COOH-terminal domain contains a high-affinity lipid binding site, but in addition an electrostatic interaction is required as a first step in the process of penetration into negatively charged DLPG films. In contrast to the constructs containing the ionophoric domain, the NH2-terminal domain alone has no fusogenic activity for liposomes. These results are discussed with regard to the mechanism of entry and action of colicin A in sensitive cells. Our results suggest the existence of a pH-dependent interaction between the receptor binding domain (amino acid residues 172-388) and the pore-forming domain of colicin A (amino acid residues 389-592).

Binding Sites↗
PubMed1989

Crystallographic phases through genetic engineering: experiences with colicin A.

Colicins are antibiotic proteins that kill sensitive Escherichia coli cells. The structure of the pore-forming fragment of colicin A has been solved to 2.5 A resolution using the techniques of X-ray crystallography and genetic engineering. Site-directed mutagenesis was used to construct a number of cysteine-containing mutant proteins, one of which yielded an excellent mercurial derivative. Our experiences suggest strategies for obtaining useful heavy-atom derivatives for protein crystallography using genetic engineering techniques.

Amino Acid Sequence↗
PubMed1989

Comparison of the uptake systems for the entry of various BtuB group colicins into Escherichia coli.

Colicins A, E1, E2 and E3 belong to the BtuB group of colicins. The NH2-terminal region of colicin A is required for translocation, and defects in this region cannot be overcome by osmotic shock of sensitive cells. In addition to BtuB, colicin A requires OmpF for efficient uptake by sensitive cells. The roles of BtuB and OmpF in translocation and binding to the receptor of the colicins A, E1, E2 and E3 were compared. The results suggest that for colicin A OmpF is used both as a receptor and for translocation across the outer membrane. In contrast, for colicin E1, OmpF is used neither as a receptor nor for translocation. For colicins E2 and E3, the situation is intermediate: only BtuB is used as a receptor but both BtuB and OmpF are involved in the translocation step.

Bacterial Outer Membrane Proteins↗
PubMed1989

Topology and function of the integral membrane protein conferring immunity to colicin A.

The topology of the integral membrane protein Cai (colicin A immunity protein), which is required to protect producing cells from the pore-forming colicin A, was analysed using fusions to alkaline phosphatase. The properties of these fusion proteins support the model for Cai topology previously proposed on theoretical grounds. The protein was found to contain four transmembrane sequences and its N- and C-terminal regions were found to be directed towards the cytoplasm. Oligonucleotide-directed mutagenesis and sequence comparisons between Cai, Cbi (colicin B immunity protein), and Cni (colicin N immunity protein) were carried out to determine the functional regions of Cai. The possible roles of the various regions of Cai in its protective function and in its topological organization are discussed.

Alkaline Phosphatase↗
PubMed1988

The membrane channel-forming colicin A: synthesis, secretion, structure, action and immunity.

The study of colicin release from producing cells has revealed a novel mechanism of secretion. Instead of a built-in 'tag', such as a signal peptide containing information for secretion, the mechanism employs coordinate expression of a small protein which causes an increase in the envelope permeability, resulting in the release of the colicin as well as other proteins. On the other hand, the mechanism of entry of colicins into sensitive cells involves the same three stages of protein translocation that have been demonstrated for various cellular organelles. They first interact with receptors located at the surface of the outer membrane and are then transferred across the cell envelope in a process that requires energy and depends upon accessory proteins (TolA, TolB, TolC, TolQ, TolR) which might play a role similar to that of the secretory apparatus of eukaryotic and prokaryotic cells. At this point, the type of colicin described in this review interacts specifically with the inner membrane to form an ion channel. The pore-forming colicins are isolated as soluble proteins and yet insert spontaneously into lipid bilayers. The three-dimensional structures of some of these colicins should soon become available and site-directed mutagenesis studies have now provided a large number of modified polypeptides. Their use in model systems, particularly those in which the role of transmembrane potential can be tested for polypeptide insertion and ionic channel gating, constitutes a powerful handle with which to improve our understanding of the dynamics of protein insertion into and across membranes and the molecular basis of membrane excitability. In addition, their immunity proteins, which exist only in one state (membrane-inserted) will also contribute to such an understanding.

Amino Acid Sequence↗
PubMed1988

Transcriptional terminators in the caa-cal operon and cai gene.

We have analysed by S1 nuclease mapping the in vivo termination sites of transcription of the caa-cal operon and cai gene. The termination region for caa mRNA (T1A terminator) features characteristics of a rho-independent terminator. This terminator is a convergent transcription terminator, its complementary secondary structure being present at the 3'-end of cai mRNA. The caa-cal mRNA terminator (T2A terminator) has a stable potential secondary structure and shows homology with rho-dependent terminators. In vitro transcription of caa-cal operon demonstrated that the two terminators T1A and T2A are efficient. The 3'-ends of the mRNAs which end at T1A and T2A were analysed by S1 mapping with total RNA purified from a mutant strain deficient in exoribonuclease activities, in particular RNase II. The results suggest that the potential secondary structures of T1A and T2A are sufficiently stable to prevent 3'-end degradation by RNase II. On the other hand, the T2A terminator should be efficient enough to stop transcription through the downstream DNA region involved in pColA replication.

Base Sequence↗
PubMed1988

DNA sequences required to induce localized conversion in Streptococcus pneumoniae transformation.

In pneumococcal transformation a particular point mutation belonging to the amiA locus is able markedly to enhance recombination frequency when crossed with any other markers of this gene. This results from a polarized conversion of the mutation towards the wild-type sequence. In this report, by site-directed oligonucleotide mutagenesis, we have generated a series of mutants showing various degrees of conversion. We have found that the substitution 5'-ATTCAT----5'-ATTAAT is a sufficient signal for localized conversion. Changing individual bases within this sequence results in decreased conversion frequencies to levels that depend on the mutation, suggesting that there is a family to related sequences which may act as a substrate for a conversion system. Moreover, the length over which this conversion occurs has been estimated to be 12 base pairs on the average.

Base Sequence↗
PubMed1988

Use of a foreign epitope as a "tag" for the localization of minor proteins within a cell: the case of the immunity protein to colicin A.

The immunity protein to colicin A (Cai), which is constitutively expressed at a very low level in Escherichia coli strains, has been studied in recombinant plasmid constructs allowing expression of various immunity fusion proteins under the control of inducible promoters. The 13-amino acid NH2-terminal region of Cai was substituted by polypeptides from beta-galactosidase or from colicin A. Upon induction of the chimeric proteins, the rate of expression of the immunity protein could be correlated to the level of resistance to colicin A. The immunity protein has been "tagged" with an epitope from the colicin A protein for which a monoclonal antibody is available. Using this technique, we have directly demonstrated that the immunity protein is located in the cytoplasmic membrane. The results indicate that the NH2-terminal region of Cai is directed toward the cytoplasm and is probably not required for Cai insertion into the membrane or for its function.

Antibodies, Bacterial↗
PubMed1988

Functional domains of colicin A.

A large number of mutations which introduce deletions in colicin A have been constructed. The partially deleted colicin A proteins were purified and their activity in vivo (on sensitive cells) and in vitro (in planar lipid bilayers) was assayed. The receptor-binding properties of each protein were also analysed. From these results, we suggest that the NH2-terminal region of colicin A (residues 1 to 172) is involved in the translocation step through the outer membrane. The central region of colicin A (residues 173 to 336) contains the receptor-binding domain. The COOH-terminal domain (residues 389 to 592) carries the pore-forming activity.

Binding Sites↗
PubMed1987

Extracellular release of colicin A is non-specific.

The possible involvement of topogenic export sequences within the colicin A polypeptide chain has been investigated. Different constructs have been made using various techniques to introduce deletions in the central and NH2-terminal regions of colicin A. Together, these deletions span the region from amino acid 15 to the end of the protein. None of these regions was found to be required for extracellular release or had any effect on the efficiency of this process. By inserting a termination codon, a Shine-Dalgarno sequence and an initiation codon into the gene for colicin A, the NH2-terminal and central plus COOH-terminal domains could be demonstrated to be released to the same extent when produced as separate polypeptides as when produced as linked ones. The introduction into the COOH-terminal domain of mutations promoting cytoplasmic aggregation had no effect on the secretion of the NH2-terminal polypeptide. These results demonstrated that no specific interaction between the NH2- and COOH-terminal regions of the colicin A polypeptide chain is involved in the release of colicin A. We are led to conclude that there is no topogenic export signal in the polypeptide chain of colicin A involved in the release mechanism. Thus the process is non-specific with respect to the colicin itself and depends solely on the expression of the colicin A lysis protein (Cavard et al., 1985, 1987). The expression of the protein causes the release of not only the colicin but also many other cellular proteins, including beta-lactamase, EF-Tu, and chloramphenicol acetyltransferase.

Base Sequence↗
PubMed1987

Mismatch repair during pneumococcal transformation of small deletions produced by site-directed mutagenesis.

The genetic behaviour of short non-homologous regions has been studied during transformation of Streptococcus pneumoniae. Amethopterin-resistant mutants belonging to the amiA locus were used for these investigations. Five mutants deleted for 1-5 bp were obtained by oligonucleotide-directed mutagenesis. Their efficiency of transformation was measured using recipient strains either able to excise and repair mismatched bases (Hex+) or Hex- derivatives. Deletions or insertions of 1 and 2 bp are fully recognized by the Hex system, and are efficiently repaired whereas 3-bp deletions or insertions are only partially excised and repaired. The efficiency of repair is inversely related to the size of the non-homology. Markers with 5-bp deletions or insertions are poorly repaired and thus transform at very high frequency: similar results are obtained in reciprocal crosses. It is proposed that 1- or 2-bp deletions or insertions are included in the heteroduplex structure as transition mutations. The Hex system would detect only small deviations from the normal DNA structure.

Chromosome Deletion↗