Construction of Bacillus anthracis mutant strains producing a single toxin component

The two protein exotoxins secreted by Bacillus anthracis are composed of three distinct components: protective antigen (PA), lethal factor (LF), and (o)edema factor (EF). We have developed a genetic strategy that permits us selectively to inactivate each of the genes coding for PA, EF or LF. This strategy involved the deletion of a portion of the structural gene and the insertion of an antibiotic resistance cassette. With this technique, double mutant strains of B. anthracis producing only one toxin component have been constructed. Characterization of the mutant strains indicated that they produced the expected single toxin protein. Using a simple, two-step protocol, we have purified PA, LF and EF to homogeneity from culture supernatants. These three mutant strains are potentially powerful tools for studying the individual effect of each toxin component in vitro and in vivo.

Calmodulin-activated bacterial adenylate cyclases as virulence factors

Bordetella pertussis and Bacillus anthracis each produce a virulence-associated, calmodulin-dependent adenylate cyclase toxin, which generates increased levels of cyclic AMP in eukaryotic cells. The two proteins share sequence similarities in their catalytic domains. The remaining regions display different structural and functional organizations that account for the differences both in interaction of the two toxins with target cells and in the resulting disease symptoms.

Regulation of pag gene expression in Bacillus anthracis: use of a pag-lacZ transcriptional fusion

The production of protective antigen (PA), the common component of the two anthrax toxins, is influenced by the environment. In order to examine factors involved in its regulation, a transcriptional fusion between the promoter region of the PA gene (pag) and the lacZ gene was constructed and introduced into Bacillus anthracis Sterne. Activity of the pag promoter was followed by measuring beta-galactosidase activities under various growth and medium conditions. Expression from the pag promoter was observed throughout exponential-phase and was maximal in early stationary phase. The activity of the pag promoter was stimulated by the addition of glucose in the medium.

Structural and functional relationships between Pasteurella multocida and enterobacterial adenylate cyclases

The Pasteurella multocida adenylate cyclase gene has been cloned and expressed in Escherichia coli. The primary structure of the protein (838 amino acids) deduced from the corresponding nucleotide sequence was compared with that of E. coli. The two enzymes have similar molecular sizes and, based on sequence conservation at the protein level, are likely to be organized in two functional domains: the amino-terminal catalytic domain and the carboxy-terminal regulatory domain. It was shown that P. multocida adenylate cyclase synthesizes increased levels of cyclic AMP in E. coli strains deficient in the catabolite gene activator protein compared with wild-type strains. This increase does not occur in strains deficient in both the catabolite gene activator protein and enzyme III-glucose, indicating that a protein similar to E. coli enzyme III-glucose is involved in the regulation of P. multocida adenylate cyclase. It also indicates that the underlying process leading to enterobacterial adenylate cyclase activation has been conserved through evolution.

Contribution of individual toxin components to virulence of Bacillus anthracis

Three proteins, protective antigen (PA), lethal factor (LF), and edema factor (EF; a calmodulin-dependent adenylate cyclase), compose the lethal (PA + LF) and edema (PA + EF) toxins secreted by Bacillus anthracis. Mutant strains, each deficient in the production of one toxin component, were constructed, and their virulence was then studied. A kanamycin resistance cassette was inserted in each cya (encoding EF) and lef (encoding LF) gene, and the constructs were separately introduced into B. anthracis Sterne on a mobilizable shuttle plasmid. An EF- strain and an LF- strain were then isolated after homologous recombination with the resident toxin-encoding plasmid, pXO1. Spores from these mutants and from a previously constructed PA- mutant were used to inoculate mice, and the lethality and local edema formation were monitored. LF- or PA- mutants were not lethal even at high inocula, whereas the EF- mutant induced lethal infections. This indicates that LF in combination with PA is a key virulence factor required for lethality. Skin edema formation was observed with the LF- mutant, which produces only the combination of PA and EF. However, EF- and LF- mutants were significantly less efficient at inducing, respectively, lethality and edema than was the parental Sterne strain. These results suggest that the three toxin components might act synergistically in vivo to cause lethality and edema formation.

Structural and ligand-binding properties of a truncated form of Bacillus anthracis adenylate cyclase and of a catalytically inactive variant in which glutamine substitutes for lysine-346

A truncated, 541-residue-long, Bacillus anthracis adenylate cyclase was expressed in Escherichia coli. The purified protein (CYA 62) exhibited catalytic and CaM-binding properties identical with those of the wild-type enzyme secreted by B. anthracis. The analysis of the secondary structure of the CYA 62 protein by Fourier transform infrared spectroscopy and circular dichroism revealed the dominance of beta-type structure. The protein shows a relatively low thermal stability with the midpoint denaturation temperature at 45 degrees C. A catalytically inactive variant of CYA 62 in which Gln substituted for Lys-346 (CYA 62 K346Q) was comparatively analyzed for its secondary structure and thermal stability, as well as ligand-binding properties with fluorescent derivatives of ATP and calmodulin. The K346Q variant of CYA 62 has a similar secondary structure and comparable calmodulin binding properties to those of the parent protein and exhibits only slightly reduced thermal stability (the apparent midpoint denaturation temperature is at 43 degrees C). Despite these similarities, the binding of 3'-anthraniloyl-2'-deoxy-ATP (a fluorescent ATP analogue) to the modified protein is severely impaired, from which we conclude that the prime function of Lys-346 in the wild-type enzyme from B. anthracis is to ensure tight binding of the nucleotide substrate to the active site.

Binding of 3'-anthraniloyl-2'-deoxy-ATP to calmodulin-activated adenylate cyclase from Bordetella pertussis and Bacillus anthracis

3'-Anthraniloyl-2'-deoxyadenosine 5'-triphosphate (Ant-dATP), a fluorescent analogue of ATP, was tested as a probe for the nucleotide-binding site of calmodulin (CaM)-activated adenylate cyclases from Bordetella pertussis (BPCYA47) and Bacillus anthracis (BACYA62). Ant-dATP competitively inhibited both bacterial enzymes expressed in Escherichia coli (ki approximately 10 microM). Binding of the analogue to adenylate cyclase was monitored by equilibrium dialysis and by an increase in its fluorescence emission at 420 nm upon excitation at 330 nm. Whereas the fluorescence of Ant-dATP was little influenced by divalent cations, CaM, or adenylate cyclase alone, the Ca2+.CaM.cyclase complex increased up to 4 times the quantum yield of Ant-dATP. Binding of the analogue to the catalytic site of BPCYA47 and BACYA62 was specific as shown by its displacement with ATP or 3'-dATP. Our results substantiate the role of CaM in favoring substrate binding to CaM-activated enzymes.

Construction and characterization of a protective antigen-deficient Bacillus anthracis strain

The pag gene coding for protective antigen (PA), one of the three toxin components of Bacillus anthracis, has been cloned into the mobilizable shuttle vector pAT187 and transferred by conjugation from Escherichia coli to B. anthracis. Using this strategy, an insertionally mutated pag gene constructed and characterized in E. coli, was introduced into B. anthracis Sterne strain. This transconjugant was used to select a recombinant clone (RP8) carrying the inactivated pag gene on the toxin-encoding plasmid, pXO1. Strain RP8 was deficient for PA while still producing the two other toxin components, i.e. lethal factor (LF) and edema factor (EF). In contrast to spores from the wild-type Sterne strain, spores prepared from RP8 were totally non-lethal in mice. These results clearly establish the central role played by PA in B. anthracis pathogenicity.

Characterization of ATP and calmodulin-binding properties of a truncated form of Bacillus anthracis adenylate cyclase

The Bacillus anthracis cya gene encodes a calmodulin-dependent adenylate cyclase. A deletion cya gene product obtained by removing 261 codons at the 5' end was expressed in a protease-deficient lon- E. coli strain and purified to homogeneity. This truncated enzyme (CYA 62) exhibits catalytic and calmodulin-binding properties similar to the properties of wild-type adenylate cyclase from B. anthracis culture supernatants, i.e., a kcat of 1100 s-1 at 30 degrees C and pH 8, an apparent Km for ATP of 0.25 mM, and a Kd for bovine brain calmodulin of 23 nM. The calmodulin-binding domain of the CYA 62 truncated enzyme was labeled with a cleavable radioactive photoaffinity cross-linker coupled to calmodulin. The labeled CYA 62 protein was then cleaved with cyanogen bromide and N-chlorosuccinimide. We show that the calmodulin-binding domain of B. anthracis adenylate cyclase is located within the last 150 amino acid residues of the protein. A further deletion at the 3' end of the CYA 62 coding sequence yielded an adenylate cyclase species (CYA 57) lacking 127 C-terminal amino residues. CYA 57, still sensitive to activation by high concentrations of calmodulin, exhibits less than 0.1% of the specific activity of CYA 62. Binding of 3'dATP (a competitive inhibitor) to CYA 62 was determined by equilibrium dialysis. In the absence of calmodulin, binding of the ATP analogue to this truncated protein was severely impaired, which explains, at least in part, the absolute requirement for calmodulin for the catalytic activity of B. anthracis adenylate cyclase.

Age variation in the association between angiographic coronary disease and angina from the Coronary Artery Surgery Study (CASS)

Between July 1974 and May 1979, 19,153 non-randomized patients without prior cardiac surgery and with chest pain were studied angiographically and enrolled in the Coronary Artery Surgery Study (CASS). The primary question addressed by this paper is: for fixed levels of coronary artery disease, are the presence and severity of angina pectoris greater for older than for younger patients? For those with the same extent of disease, older patients were more likely to have angina and to exhibit more severe symptoms. After adjustment for covariates using logistic regression analysis, age was found to be an important, independent predictor of the presence and severity of angina. There are many possible explanations for these findings, although physiologic factors related to aging, the disease process, and deconditioning associated with an increased sedentary life style seem most reasonable. Another possibility has to do with referral patterns for study and the prevalence of angina in the different age groups.

Immunity protein is not required for the bactericidal activity of colicin E3

Plasmid pLAX3, carrying the colicin E3 gene, was used to direct the in vitro synthesis of a colicin E3* molecule totally devoid of its immunity protein. We established that this molecule is able to kill sensitive Escherichia coli cells in the total absence of immunity protein. Therefore, all of the information required for colicin E3 action is located on the colicin polypeptide itself. Furthermore, our studies indicated that immunity protein protects the C-terminal enzymatic part of native colicin E3 protein against proteolytic degradation before or during its translocation across the cell envelope. These results are discussed in relation to the mode of entry of colicin E3 into bacterial cells.

Identification of a common domain in calmodulin-activated eukaryotic and bacterial adenylate cyclases

Bordetella pertussis and Bacillus anthracis, two taxonomically distinct bacteria, secrete adenylate cyclase toxins that are activated by the eukaryotic protein calmodulin. The two enzymes contain a well-conserved stretch of 24 amino acid residues [Escuyer et al. (1988) Gene 71, 293-298]. Antibodies have been obtained against two synthetic heptadecapeptides, covering part of the conserved sequences. The anti-peptide antibodies specifically reacted in Western blots with the rat brain adenylate cyclase as well as with the two bacterial enzymes. Anti-rat brain adenylate cyclase serum contained antibodies that were retained by the immobilized peptides, and the affinity-purified antibodies yielded the same recognition pattern of the eukaryotic enzyme as did the unfractionated serum. These results indicate that the eukaryotic adenylate cyclase contains an epitope closely related to that specified by the conserved bacterial sequence. The synthetic peptides and the bacterial adenylate cyclases appeared to compete for ATP (KD of the ATP-peptide complex ca. 0.2 mM), suggesting that the conserved sequence may be part of the substrate binding site in these two enzymes.

Structural homology between virulence-associated bacterial adenylate cyclases

The primary structure of the calmodulin-sensitive adenylate cyclase toxin from Bacillus anthracis has been determined from the corresponding nucleotide sequence and compared to that of the homologous toxin secreted by Bordetella pertussis. The cya gene of Bacillus anthracis encodes an 800 amino acid (aa) protein beginning with an N-terminal signal peptide. The central part of the B. anthracis adenylate cyclase includes a region of striking homology with the N-terminal part of the B. pertussis enzyme. In this region a particularly well conserved 24-aa peptide and two other less homologous peptides have been identified. These data corroborate the immunological relatedness of the two enzymes and suggest that the two prokaryotic calmodulin-sensitive adenylate cyclases originate from a common ancestor.

Cloning and expression of the calmodulin-sensitive Bacillus anthracis adenylate cyclase in Escherichia coli

The adenylate cyclase gene of Bacillus anthracis, encoding the edema factor, a component of anthrax toxin, has been cloned and expressed in Escherichia coli. Clones were selected by their capacity to complement the cyclase deficiency (cya-) of an E. coli strain expressing the eukaryotic protein calmodulin, an essential activator of B. anthracis adenylate cyclase. The protein expressed in E. coli was shown to exhibit adenylate cyclase activity only in the presence of calmodulin. Experiments using a coupled in vitro transcription-translation system revealed that the protein synthesized from the cloned DNA fragment was enzymatically active, upon addition of calmodulin, and could be immunoprecipitated by antibodies directed against purified Bordetella pertussis adenylate cyclase toxin. This indicates that the two calmodulin-dependent adenylate cyclase toxins are immunologically related.

DNA sequence analysis of three missense mutations affecting colicin E3 bactericidal activity

We have determined the nucleotide sequence changes caused by three missense mutations leading to the production of inactive colicin E3 proteins. The ceaC1 mutation, affecting the translocation of colicin E3 through bacterial membranes, is caused by a serine to phenylalanine change at position 37 within the glycine-rich region at the N-terminal part of colicin E3. This confirms previous results suggesting a role for this domain in colicin uptake by sensitive cells. The ceaC2 and ceaC3 mutations, abolishing colicin E3 RNase activity, affect the C-terminal enzymatic domain of the molecule. In the ceaC2 mutant, serine at position 529 was converted to leucine. The ceaC3 mutation replaced a glycine residue at position 524 with an aspartic acid residue. The two mutations ceaC2 and ceaC3 yield information on the amino acid residues involved in the RNase activity of colicin E3.

A pH-induced increase in hydrophobicity as a possible step in the penetration of colicin E3 through bacterial membranes

Exposure to low pH triggers an increase in the hydrophobicity of the colicin E3 molecule. Using a [3H] Triton X-100 binding assay we have shown that the amount of detergent (at supramicellar concentrations) associated with colicin E3 increased dramatically at pH 3.8 and below. Interaction of colicin E3 with asolectin vesicles was monitored by following its cross-linking with two different photoactivatable radioactive phospholipid analogues. At neutral pH colicin E3 was cross-linked with the phospholipid probing the membrane surface whereas at pH 4.5 and below, the bacteriocin reacted with the phospholipid probing the hydrophobic core of the bilayer. With the use of phase partitioning of proteins in Triton X-114 it was shown that at acidic pH whole colicin E3 and its immunity protein segregated in the detergent phase. After trypsin digestion of the colicin-immunity complex, the N-terminal portion of E3 (T1) and the immunity partitioned in the detergent phase at low pH. In contrast, the enzymic domain of the colicin (T2) remained in the aqueous phase and was recovered in a highly active form as a consequence of its dissociation from the immunity protein. These results are discussed in relation to the mechanism of entry of colicin E3 into bacterial cells.

Myotonic dystrophy and pregnancy: a review

The previous reports of 20 women with myotonic dystrophy and pregnancy are reviewed, and a new case report added. Myotonic dystrophy is often unrecognized in early life due to vague symptoms, and is often first diagnosed during pregnancy which is known to worsen the main features of muscular weakness and myotonia. Complications of pregnancy and delivery are frequent and serious and should be known to all those dealing with pregnant women. A history of fetal wastage or a child suffering from symptoms of congenital myotonic dystrophy may be a clue to the diagnosis and these patients should be closely followed until safe delivery. The neonatologist should be involved as feeding and respiratory problems in the neonate may indicate that the infant is affected.

Genetic analysis of the functional relationship between colicin E3 and its immunity protein

Partial deletions in the immunity gene of the colicin E3 operon were used to study possible functions of the immunity protein besides protection against exogenous colicin. Nuclease BAL-31 was used to create a series of carboxyl-terminal deletions of the immunity gene. Mutants displaying lowered immunity against exogenous colicin were found, and six that had reduced but detectable levels of immunity were chosen for further analysis. DNA sequence analysis of the deletions showed that all six terminated within the last five codons of the immunity gene. The wild-type immunity gene was replaced by each of the six mutated immunity genes in a plasmid containing an otherwise functional colicin E3 operon. Transformants containing the resulting plasmids produced smaller colonies on solid medium and grew more slowly in liquid culture than transformants carrying the wild-type colicin and immunity genes. This result suggested that immunity protein was required to protect the cell against endogenous colicin E3. This idea was confirmed in experiments in which the colicin E3 and immunity genes were independently cloned on two compatible plasmid vectors.

A technique for integrating any DNA fragment into the chromosome of Escherichia coli

We describe a technique that allows the insertion of any DNA fragment into the EcoRI-site-containing malPpa, the promoter of malPQ, one of the three maltose operons of Escherichia coli. DNA fragments were cloned into the unique EcoRI site of the pBR322-derived plasmid pOM40, which carries malPpa. In the next step these fragments were transposed into the chromosome by homologous recombination events occurring on both sides of malPp. Cells in which such insertion of the entire recombinant plasmid have occurred can be conveniently selected. Excision and curing of the vector plasmid could then occur spontaneously at a high frequency, leaving behind the inserted fragment that can be manipulated as any chromosomal marker. When the inserted fragment contains a properly positioned promoter, its promoting activity can be estimated by assaying amylomaltase, the product of malQ. When required, the inserted fragment can be easily transferred back onto pOM40. As examples of application we have transferred two different fragments into the chromosome of E. coli: one contained the ceaC-ceiC operon, which encodes colicin E3 and its immunity protein, and the other contained the lac promoter of E. coli.

Nucleotide sequence for the catalytic domain of colicin E3 and its immunity protein. Evidence for a third gene overlapping colicin

We have determined the nucleotide sequence of a segment of Co1E3 DNA coding for the carboxyl-terminal, catalytic peptide of colicin E3 and for the immunity protein. The end of the colicin E3 gene is separated from the beginning of the immunity gene by a nine-basepair intercistronic region, suggesting the two genes are expressed as a single transcriptional unit. The immunity gene is expressed, however, in E. coli strains containing Co1E3-pBR322 hybrid plasmids deleted for the 5'-end of the colicin gene. The DNA sequence also contains an unexpected open reading frame (ORF). This ORF is contained within the colicin gene and is in the +1 reading frame with respect to that gene. Plasmids containing the ORF, directed the synthesis of an 11 kilodalton protein in a cell-free, transcription-translation system.

Prognostic value of angiographic indices of coronary artery disease from the Coronary Artery Surgery Study (CASS)

The Coronary Artery Surgery Study, CASS, enrolled 24,959 patients between August 1975 and June 1979 who were studied angiographically for suspected coronary artery disease. This paper compares the prognostic value for survival without early elective surgery of eight different indices of the extent of coronary artery disease: the number of diseased vessels, two indices using the number of proximal arterial segments diseased, two empirically generated indices from the CASS data, and the published indices of Friesinger, Gensini, and the National Heart and Chest Hospital, London. All had considerable prognostic information. Typically 80% of the prognostic information in one index was also contained in another. Our analysis shows that good prediction from angiographic data results from a combination of left ventricular function and arteriographic extent of disease. Prognosis may reasonably be obtained from three simple indices: the number of vessels diseased, the number of proximal arterial segments diseased, and a left ventricular wall motion score. These three indices account for an estimated 84% of the prognostic information available. 6-yr survival varies between 93 and 16% depending upon the values of these three indices.

The BtuB group col plasmids and homology between the colicins they encode

Colicins A, E1, E2, E3, E4, E5, E6, and E7 exhibited reduced activity against BtuB mutants of Escherichia coli K-12 and also against wild-type cells in the presence of vitamin B12. Plasmids encoding representatives of these colicins were specifically immune to high levels of the homologous colicin. Col(+) cells grown in media containing mitomycin C accumulated large amounts of colicin polypeptide. ColE2(+), ColE3(+), ColE4(+), ColE5(+), and ColE6(+) cultures also synthesized large amounts of second, lower-molecular-weight protein under these conditions. Colicins E2 through E7, but not A or E1, reacted with antiserum raised against purified colicin E3. Colicins E2 and E7 induced synthesis of beta-galactosidase encoded by lacZ under the control of the colicin Ib gene promotor on a derivative of Col plasmid ColIb.P9. This promotor is usually active only when the cells are treated with agents which damage DNA or block replication. Plasmids encoding various mutant forms of colicin E3 (M. Mock and M. Schwartz, J. Bacteriol. 142:384-390, 1980) recombined with ColE2, ColE4, ColE5, or ColE6 plasmids at a frequency of 10(-4) per cell to produce a colicin active against ColE2(+), E4(+), E5(+), or E6(+) cells. ColE5 and ColE6 plasmids recombined with ColE3 plasmids bearing mutations affecting colicin E3 receptor recognition, envelope penetration, and catalytic activities. ColE2 and ColE4 plasmids recombined only with ColE3 plasmids bearing mutations affecting receptor recognition and envelope penetration. Recombinants between mutant ColE3 plasmids and ColA, ColE1, or ColE7 plasmids were not detected. We propose the designation BtuB group for the colicins described here, and we divide the group into two classes comprising colicins A and E1, which act on the cytoplasmic membrane, and the related colicins E2 through E7, which have known or putative nuclease activities.

Preservation of the myocardium during coronary artery bypass grafting

The influence of three methods of myocardial preservation used during coronary artery bypass grafting on operative mortality and perioperative myocardial infarction was evaluated in seven institutions participating in the Coronary Artery Surgery Study (CASS). Both operative mortality and perioperative infarctions were comparable with either normothermic and topical hypothermic myocardial preservation. The addition of potassium cardioplegia to hypothermia lowered both operative mortality and perioperative myocardial infarction (p less than 0.01 and p less than 0.001, respectively). Stepwise multivariate discriminant analysis revealed that the high-risk clinical and angiographic variables were the most important determinants of operative mortality, followed by surgical priority and the use of potassium cardioplegia. However, none of the clinical, angiographic and surgical variables other than the use of potassium cardioplegia influenced the incidence of perioperative myocardial infarction.

Mutations which affect the structure and activity of colicin E3

Among 69 ColE3 mutant plasmids selected on the basis of their inability to produce an active colicin, seven (cop-1 to cop-7) were found to bear a mutation affecting the structural gene for colicin. Three of these (cop-1, cop-2 and cop-3) lead to the production of an inactive colicin molecule which has the same molecular weight as wild-type colicin E3 (67,000). These three inactive colicins are still able to interact with the outer membrane receptor. The cop-1 protein retained the ability to inhibit protein synthesis in vitro and therefore seems specifically affected in it ability to penetrate the cell envelope. The cop-2 and cop-3 proteins lost the ability to inhibit protein synthesis in vitro, and activity which is normally associated with the C-terminal part of the colicin molecule. On the basis of this and further evidence, it is suggested that the cop-2 and cop-3 mutations affect the structure of the C-terminal part of the colicin molecule. The other four mutations (cop-4 to cop-7) lead to the production of colicin-related polypeptides of lower molecular weight (29,000 to 45,000) which display a reaction of partial immunological identity with wild-type colicin. These four polypeptides are unable to interact with the cell surface receptor. Three of these mutants are shown to carry a nonsense mutation.