Development of antitoxin with each of two complementary fragments of Clostridium botulinum type B derivative toxin

A Novel Inhibitor Prevents the Peripheral Neuroparalysis of Botulinum Neurotoxins

Botulinum neurotoxins (BoNTs) form a large class of potent and deadly neurotoxins. Given their growing number, it is of paramount importance to discover novel inhibitors targeting common steps of their intoxication process. Recently, EGA was shown to inhibit the action of bacterial toxins and viruses exhibiting a pH-dependent translocation step in mammalian cells, by interfering with their entry route. As BoNTs act in the cytosol of nerve terminals, the entry into an appropriate compartment wherefrom they translocate the catalytic moiety is essential for toxicity. Herein we propose an optimized procedure to synthesize EGA and we show that, in vitro, it prevents the neurotoxicity of different BoNT serotypes by interfering with their trafficking. Furthermore, in mice, EGA mitigates botulism symptoms induced by BoNT/A and significantly decreases the lethality of BoNT/B and BoNT/D. This opens the possibility of using EGA as a lead compound to develop novel inhibitors of botulinum neurotoxins.

The long journey of botulinum neurotoxins into the synapse

Botulinum neurotoxins (BoNT) cause the disease botulism, a flaccid paralysis of the muscle. They are also very effective, widely used medicines applied locally in sub-nanogram quantities. BoNTs are released together with several non-toxic, associated proteins as progenitor toxin complexes (PCT) by Clostridium botulinum to become highly potent oral poisons ingested via contaminated food. They block the neurotransmission in susceptible animals and humans already in nanogram quantities due to their specific ability to enter motoneurons and to cleave only selected neuronal proteins involved in neuroexocytosis. BoNTs have developed a sophisticated strategy to passage the gastrointestinal tract and to be absorbed in the intestine of the host to finally attack neurons. A non-toxic non-hemagglutinin (NTNHA) forms a binary complex with BoNT to protect it from gastrointestinal degradation. This binary M-PTC is one component of the bi-modular 14-subunit ∼760 kDa large progenitor toxin complex. The other component is the structurally and functionally independent dodecameric hemagglutinin (HA) complex which facilitates the absorption on the intestinal epithelium by glycan binding. Subsequent to its transcytosis the HA complex disrupts the tight junction of the intestinal barrier from the basolateral side by binding to E-cadherin. Now, the L-PTC can also enter the circulation by paracellular routes in much larger quantities. From here, the dissociated BoNTs reach the neuromuscular junction and accumulate via interaction with polysialo gangliosides, complex glycolipids, on motoneurons at the neuromuscular junction. Subsequently, additional specific binding to luminal segments of synaptic vesicles proteins like SV2 and synaptotagmin leads to their uptake. Finally, the neurotoxins shut down the synaptic vesicle cycle, which they had exploited before to enter their target cells, via specific cleavage of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, which constitute the core components of the cellular membrane fusion machinery.

Towards new uses of botulinum toxin as a novel therapeutic tool

The uses of botulinum toxin in the fields of neurology, ophthalmology, urology, rehabilitation medicine and aesthetic applications have been revolutionary for the treatment of patients. This non-invasive therapeutic has continually been developed since first discovered in the 1970s as a new approach to what were previously surgical treatments. As these applications develop, so also the molecules are developing into tools with new therapeutic properties in specific clinical areas. This review examines how the botulinum toxin molecule is being adapted to new therapeutic uses and also how new areas of use for the existing molecules are being identified. Prospects for future developments are also considered.

Immune recognition of botulinum neurotoxin B: antibody-binding regions on the heavy chain of the toxin

The purpose of this work was to map the continuous regions recognized by human, horse and mouse anti-botulinum neurotoxin B (BoNT/B) antibodies (Abs). We synthesized a panel of sixty 19-residue peptides (peptide C31 was 24 residues) that overlapped consecutively by 5 residues and together encompassed the entire heavy chain of BoNT/B (H/B, residues 442-1291). Abs from the three host species recognized similar, but not identical, peptides. There were also peptides recognized by two or only by one host species. Where a peptide was recognized by Abs of more than one host species, these Abs were at different levels among the species. Human, horse and mouse Abs bound, although in different amounts, to regions within peptides 736-754, 778-796, 848-866, 932-950, 974-992, 1058-1076 and 1128-1146. Human and horse Abs bound to peptides 890-908 and 1170-1188. Human and mouse Abs recognized peptides 470-488/484-502 overlap, 638-656, 722-740, 862-880, 1030-1048, 1072-1090, 1240-1258 and 1268-1291. We concluded that the antigenic regions localized with the three antisera are quite similar, exhibiting in some cases a small shift to the left or to the right. This is consistent with what is known about protein immune recognition. In the three-dimensional structure, the regions recognized on H/B by anti-BoNT/B Abs occupied surface locations and analysis revealed no correlation between these surface locations and surface electrostatic potential, hydrophilicity, hydrophobicity, or temperature factor. A region that bound mouse Abs overlapped with a recently defined site on BoNT/B that binds to mouse and rat synaptotagmin II, thus providing a molecular explanation for the blocking (protecting) activity of these Abs. The regions thus localized afford candidates for incorporation into a synthetic vaccine design.

Mucosal vaccine development for botulinum intoxication

Botulism has classically been considered to be a food- and water-borne disease. However, it was recently classified by the US National Institute of Allergy and Infectious Diseases (National Institute of Health) and the US Centers for Disease Control and Prevention as a Category A agent. Thus, the botulinum exotoxin, a neurotoxin, could be easily disseminated by bioterrorists through the air-borne route with a high morbidity and mortality rate. In this regard, a high priority should be given to the development of a safe and effective mucosal vaccine to protect against botulinum neurotoxins (BoNTs) since it is well known that the mucosal immune system is the first line of defense against major pathogens. Further, mucosal immunization has been shown to induce both mucosal and systemic immunity to pathogens. By contrast, the current injection-type vaccine only provides protective immunity in the systemic compartment. Clearly, the development of a safe and effective mucosal vaccine against this toxin should be a high priority. In this regard, it has been shown that both nasal and oral immunization approaches have been taken in order to protect from BoNT intoxication. In this article, we will discuss the importance of the development of a mucosal vaccine against botulinum and introduce current aspects of BoNT mucosal vaccines, which show that they effectively prevent mucosal BoNT intoxication.

Mapping of the antibody-binding regions on the HN-domain (residues 449-859) of botulinum neurotoxin A with antitoxin antibodies from four host species. Full profile of the continuous antigenic regions of the H-chain of botulinum neurotoxin A

Previously, we mapped the antibody (Ab) and T-cell recognition regions on the HC domain (residues 855-1296) of the 848-residue heavy (H) chain of botulinum neurotoxin A (BoNT/A). We have mapped here the HN-domain (residues 449-859) regions that bind protective anti-BoNT/A Abs raised in four different species. We synthesized, purified, and characterized 29 19-residue peptides that spanned the entire HN and overlapped consecutively by 5 residues, and also region L218-231 around the L-chain's substrate-binding site. Human, horse, mouse, and chicken anti-BoNT/A Abs did not bind to the L-peptide but recognized similar HN regions within peptides 519-537/533-551/547-565/561-579 (with slight left- or right-shifts), 743-761, 785-803, and 813-831/827-845 overlap. Recognition of other peptides that bound lower Ab levels showed similarities and also some differences. Peptide 463-481, strongly immunodominant with horse antisera, did not bind human, mouse, and chicken Abs. However, peptide 449-467 bound Abs in these three antisera, and the region may have shifted to the right (peptide 463-481) with horse Abs. The overlap 659-677/673-691 reacted strongly with human Abs whereas with mouse and chicken antisera, only peptide 673-691 showed low reactivity. Horse antisera had no detectable Ab binding to region(s) 659-691. The Ab-recognition regions on the H chain occupy surface locations in BoNT/A three-dimensional structure, but the great part of the surface is not immunogenic. Regions recognized by the protective antisera of the four different species are prime candidates for inclusion in synthetic vaccine designs.

Botulinum toxin type B (Myobloc): pharmacology and biochemistry

Purified toxin complexes have found a niche in the treatment of clinical disorders involving muscle hyperactivity. This report describes the fundamental biochemical properties of the commercially available form of Botulinum Toxin Type B and compares these attributes to the Type A form of the Toxin. Both neurotoxins act to inhibit the release of acetylcholine at the neuromuscular junction, causing muscle paralysis. The different serotypes are structurally and functionally similar; however, specific differences in neuronal acceptor binding sites, intracellular enzymatic sites, and species sensitivities suggest that each serotype is its own unique pharmacologic entity. Data are provided on the biochemical properties and long-term stability of the Type B product, which is uniquely formulated as a liquid product.

Botulinum toxin type B: an overview of its biochemistry and preclinical pharmacology

Produced by Clostridium botulinum, botulinum toxins are high molecular weight protein complexes consisting of the neurotoxin and additional nontoxic proteins that function to protect the toxin molecule. The neurotoxin acts to inhibit the release of acetylcholine at the neuromuscular junction, causing muscle paralysis. Purified toxin complexes have found a niche in the treatment of clinical disorders involving muscle hyperactivity. The different serotypes are structurally and functionally similar; however, specific differences in neuronal acceptor binding sites, intracellular enzymatic sites, and species sensitivities suggest that each serotype is its own unique pharmacologic entity. Recently, botulinum toxin type B has been developed as a liquid formulation to avoid the lyophilization (vacuum-drying) and reconstitution processes associated with decreasing the potency and stability of current type A toxin preparations. Biochemical tests were conducted to evaluate the quality of toxin in this formulation. In 3 consecutive manufacturing lots, the botulinum toxin type B complex was found to be highly purified, intact, uniform, and consistent from lot to lot. Also, it showed long-term stability at refrigerator and room temperatures (2 to 25 degrees C). Electrophysiologic studies in cynomolgus monkeys showed that botulinum toxin type B is effective in paralyzing injected muscle groups, with minimal spread to relatively distant noninjected muscles.

Botulinum toxin type B: an overview of its biochemistry and preclinical pharmacology

Produced by Clostridium botulinum, botulinum toxins are high molecular weight protein complexes consisting of the neurotoxin and additional nontoxic proteins that function to protect the toxin molecule. The neurotoxin acts to inhibit the release of acetylcholine at the neuromuscular junction, causing muscle paralysis. Purified toxin complexes have found a niche in the treatment of clinical disorders involving muscle hyperactivity. The different serotypes are structurally and functionally similar; however, specific differences in neuronal acceptor binding sites, intracellular enzymatic sites, and species sensitivities suggest that each serotype is its own unique pharmacologic entity. Recently, botulinum toxin type B has been developed as a liquid formulation to avoid the lyophilization (vacuum-drying) and reconstitution processes associated with decreasing the potency and stability of current type A toxin preparations. Biochemical tests were conducted to evaluate the quality of toxin in this formulation. In 3 consecutive manufacturing lots, the botulinum toxin type B complex was found to be highly purified, intact, uniform, and consistent from lot to lot. Also, it showed long-term stability at refrigerator and room temperatures (2 to 25 degrees C). Electrophysiologic studies in cynomolgus monkeys showed that botulinum toxin type B is effective in paralyzing injected muscle groups, with minimal spread to relatively distant noninjected muscles.

Endocytosis of Clostridium botulinum type B neurotoxin into rat brain synaptosomes

Clostridium botulinum type B neurotoxin cleaves VAMP (vesicle-associated membrane protein)/synaptobrevin into two fragments, which results in inhibition of neurotransmitter release. The induced fragment did not react to the antibody raised against the synthetic peptide of the amino-terminal 20 residues of VAMP-2, suggesting that the toxin treatment has caused antigenical alteration in the amino-terminal region of VAMP-2. In rat brain synaptosomes, type B neurotoxin was reduced presumably with sulfhydryls in the membrane and detected in the synaptic vesicle fraction which involved the degradation of VAMP-2 and the inhibition of neurotransmitter release. The light chain in a free form was present in the cytosol fraction. These findings suggest a possibility that type B neurotoxin endocytoses into synaptic vesicles by the recycling pathway and the light chain is penetrable through synaptic vesicle membrane. However, the amount of type B neurotoxin entrapped into synaptic vesicles appears to be extremely small, which may be attributed to a lower sensitivity of the toxin to brain synaptosomes than to peripheral nerve endings.

Characterization of Clostridium botulinum type B neurotoxin associated with infant botulism in japan

The neurotoxin of strain 111 (111/NT) associated with type B infant botulism showed antigenic and biological properties different from that (Okra/NT) produced by a food-borne botulism-related strain, Okra. The specific toxicity of 111/NT was found to be about 10 times lower than that of Okra/NT. The monoclonal antibodies recognizing the light chain cross-reacted with both neurotoxins, whereas most of the antibodies recognizing the carboxyl-terminal half of the heavy chain of Okra/NT did not react to 111/NT. Binding experiments with rat brain synaptosomes revealed that 125I-labeled 111/NT bound to a single binding site with a dissociation constant (Kd) of 2.5 nM; the value was rather lower than that (0.42 nM) of 125I-Okra/NT for the high-affinity binding site. In the lipid vesicles reconstituted with ganglioside GT1b, 125I-Okra/NT interacted with the amino-terminal domain of synaptotagmin 1 (Stg1N) or synaptotagmin 2 (Stg2N), fused with the maltose-binding protein, in the same manner as the respective full-length synaptotagmins, and the Kd values accorded with those of the low- and high-affinity binding sites in synaptosomes. However, 125I-111/NT only exhibited a low capacity for binding to the lipid vesicles containing Stg2N, but not Stg1N, in the presence of ganglioside GT1b. Moreover, synaptobrevin-2, an intracellular target protein, was digested to the same extent by the light chains of both neurotoxins in a concentration-dependent manner. These findings indicate that the 111/NT molecule possesses the receptor-recognition site structurally different from Okra/NT, probably causing a decreased specific toxicity.

The high-affinity binding of Clostridium botulinum type B neurotoxin to synaptotagmin II associated with gangliosides GT1b/GD1a

125I-labeled botulinum type B neurotoxin was shown to bind specifically to recombinant rat synaptotagmins I and II. Binding required reconstitution of the recombinant proteins with gangliosides GT1b/GD1a. Scatchard plot analyses revealed a single class of binding site with dissociation constants of 0.23 and 2.3 nM for synaptotagmin II and synaptotagmin I, respectively, values very similar to those of the high- (0.4 nM) and low-affinity (4.1 nM) binding sites in synaptosomes. The high-affinity binding of neurotoxin to synaptosomes was specifically inhibited by a monoclonal antibody recognizing with the amino-terminal region of synaptotagmin II. These results suggest that this region of synaptotagmin II participates in the formation of the high-affinity toxin binding site by associating with specific gangliosides.

Nucleotide sequence of the gene coding for non-proteolytic Clostridium botulinum type B neurotoxin: comparison with other clostridial neurotoxins

The neurotoxin gene of non-proteolytic Clostridium botulinum type B (strain Eklund 17B) was cloned as a series of overlapping polymerase chain reaction (PCR) fragments generated with primers designed to conserved regions of published botulinal toxin (BoNT) sequences. The 3' end of the gene was obtained by using primers designed to the determined sequence of non-proteolytic BoNT/B and a published downstream region of BoNT/B gene from a proteolytic strain. Translation of the nucleotide sequence derived from cloned PCR fragments demonstrated the toxin gene encodes a protein of 1291 amino acid residues. Comparative alignment of the derived BoNT/B sequence with those of other published botulinal neurotoxins revealed highest sequence relatedness with BoNT/B of proteolytic C. botulinum. The sequence identity between non-proteolytic and proteolytic BoNT/B was 97.7% for the light chain (corresponding to 10 amino acid changes) and 90.2% for the heavy chain (corresponding to 81 amino acid changes), with most differences occurring at the C-terminal end. A genealogical tree constructed from all known botulinal neurotoxin sequences revealed marked topological differences with a phylogenetic tree of C. botulinum types based upon small-subunit (16S) ribosomal RNA sequences.

Solubilization and characterization of the acceptor for Clostridium botulinum type B neurotoxin from rat brain synaptic membranes

The acceptor for Clostridium botulinum type B neurotoxin was solubilized from rat brain synaptic membrane with nonionic detergent, nonanoyl-N-methylglucamide (MEGA-9). The solubilized acceptor was assayed for the binding activity by precipitating the acceptor with acetone in the presence of phosphatidylcholine. 125Ilabeled neurotoxin specifically bound to the lipid vesicles having incorporated the acceptor together with gangliosides. The lipid vesicles having incorporated either the acceptor or gangliosides alone showed extremely low binding activity. The treatment of the solubilized acceptor with lysyl endopeptidase and glycopeptidase F but not with sialidase resulted in decreased toxin binding, indicating that the putative acceptor is a glycoprotein accompanying an N-linked carbohydrate moiety. The observations suggest also that a protein acceptor/ganglioside complex may be required to form the functional toxin receptor.

Nucleotide sequence of the gene coding for Clostridium barati type F neurotoxin: comparison with other clostridial neurotoxins

The neurotoxin gene from Clostridium barati ATCC43756 was cloned as a series of overlapping polymerase chain reaction (PCR) generated fragments using primers designed to conserve toxin sequences previously published. The toxin gene has an open reading frame (ORF) of 1268 amino acids giving a calculated molecular mass of 141,049 Da. The sequence identity between the C. barati ATCC43756 and non-proteolytic C. botulinum 202F neurotoxins is 64.2% for the light chain and 73.6% for the heavy chain. This is much lower than reported identities for the type E neurotoxins from C. botulinum and C. butyricum (96% identity between light chains and 98.8% between the heavy chains). Previously identified conserved regions in other botulinal neurotoxins were also conserved in that of C. barati. An ORF upstream of the toxin coding region was revealed. This shows strong homology to the 3' end of the gene coding for the nontoxic-nonhemagglutinin (NTNH) component of the progenitor toxin from C. botulinum type C neurotoxin.

Changes in the molecular topography of the light and heavy chains of type A botulinum neurotoxin following their separation

Botulinum neurotoxin serotype A, an approx. 150 kDa protein, is composed of two subunits, the light and heavy chains (approximately 50 and approximately 100 kDa, respectively). The neurotoxin's mode of action is believed to depend on coordinated but independent actions of the two subunit chains. The molecular environments of the aromatic amino acid residues of the dichain neurotoxin and the two isolated subunit chains were analyzed using near-ultraviolet circular dichroism (CD) (between 250 and 320 nm) and second-derivative ultraviolet absorption spectroscopy (between 240 and 320 nm) to investigate the conformational variations of the subunit chains in separated and conjugated forms. The mean residue weight ellipticities showed virtually no change (i.e., 1.7%) in the vicinities of Phe (268 nm), and only a small change (11%) around Tyr (279 nm) residues following dissociation of the subunit chains. However, significant changes (23-26%) at 286 nm as well as at 292 nm were noted, suggesting considerable alteration in the conformation of the subunits. Second-derivative ultraviolet absorption spectra indicated the degree of Tyr exposure in the dichain neurotoxin, isolated heavy and light chains at 70.7, 81.5 and 46.4%, respectively. A weighted mean of the degree of exposed Tyr residues in the separated heavy and light chains was 69.6%, virtually same as the 70.7% exposed Tyr residues observed in the intact dichain neurotoxin, indicating no difference in their Tyr exposure upon separation of the two chains. This was corroborated by the CD data which revealed only small changes in the CD signals of Tyr residues, and no alteration in those of the Phe residues following separation of the subunit chains. However, a change in the CD signal at 292 nm suggested that the conformations of Trp-containing segments of the two chains were significantly influenced upon their separation. The heavy and light chains of the neurotoxin therefore appear to exist as two semi-independent domains, in spite of being linked by disulfide and noncovalent bonds, and at least part of their conformations depends on interactions between them.

C. botulinum neurotoxin types A and E: isolated light chain breaks down into two fragments. Comparison of their amino acid sequences with tetanus neurotoxin

The flaccid paralysis in the neuromuscular disease botulism appears to depend on the coordinated roles of the approximately 50 kDa light and approximately 100 kDa heavy chain subunits of the approximately 150 kDa neurotoxic protein produced by Clostridium botulinum (J. Biol. Chem. (1987) 262, 2660 and Eur. J. Biochem. (1988) 177, 683). We observed that the light chain after separation from its conjugate heavy chain, in the presence of dithiothreitol and 2 M urea, begins to split into approximately 28 and approximately 18 kDa fragments. The other subunit-the approximately 100 kDa heavy chain following its isolation-and the parent approximately 150 kDa dichain neurotoxin do not break down under comparable conditions. This cleavage was examined in the neurotoxin serotypes A and E. The cleavage does not appear to be due to a protease. Partial amino acid sequences established that: i) the approximately 28-kDa and approximately 18-kDa fragments comprise the N- and C-terminal regions of the light chain, respectively; ii) the light chain of the neurotoxin serotypes A and E break down at precise peptide bonds; iii) the peptide bonds cleaved in serotypes A and E are five residues apart; and iv) the portions of the approximately 18 kDa fragments of serotype A and E neurotoxin sequenced so far are highly homologous to the corresponding region of tetanus neurotoxin produced by Clostridium tetani. The partial N-terminal sequence of the approximately 28 kDa fragment matches with the N-terminal sequence of the intact L chain. The 47 residues of the approximately 18-kDa fragment of type A sequenced from its N-terminal are: -Y.E.M.S.G.L.E.V.S.F.E.E.L.R.T.F.G.G.H.D.A.K.F.I.D.S.L.Q.E.N.E.F.R.L.Y.Y .Y. N.K.F.K. D.I.A.S.T.L.-. These align with those of tetanus neurotoxin beginning at its residue #259 (Tyr); the 18 underlined residues of the above 47 residues (i.e. 38%) are identical in positions between the two proteins. The 41 residues sequenced from the approximately 18 kDa fragment of type E botulinum neurotoxin are: -K.G.I.N.I.E.E.F.L. T.F.G.N.N.D.L.N.I.I.T.V.A.Q.Y.N.D.I.Y.T.N.L.L.N.D.Y.R. K.I.A.X.K. L.-.(ABSTRACT TRUNCATED AT 250 WORDS)

Botulinum neurotoxin type A radiolabeled at either the light or the heavy chain

Botulinum neurotoxin (NT) has two distinct structural regions called L and H chains (approximately 50 and approximately 100 kDa, respectively). Although the H chain is responsible for binding of the NT to neuronal cells, it is not known which of the subunits is internalized and therefore responsible for causing the blockage of acetylcholine release in susceptible neuronal cells. In this report we describe for the first time the preparation of type A NT which is selectively radiolabeled at either the L or the H chain subunit. Such NT preparations will be useful as tools for determining the distribution of L and H chains in poisoned neuronal cells and the role that each subunit plays in inducing toxicity. The L and H chains of the NT (approximately 150 kDa) were separated, purified, and then individually radiolabeled by reductive methylation of the lysine residues using [3H]- or [14C]formaldehyde. The labeled L and H chains were reconjugated with the complementary unlabeled L and H chains. Formation of -S-S- and noncovalent bonds between the L and H chains regenerated the approximately 150 kDa NT. Autoradiographs of sodium dodecyl sulfate polyacrylamide gels confirmed that each reconstituted NT preparation was labeled at only one subunit chain. NT selectively labeled at either the L or the H chain had specific radioactivities of ca. 25-30 and 45-55 microCi/mumol, respectively, and toxicity (mouse LD50/mg protein) values of 2.2 +/- 1.1 X 10(7) and 3.0 +/- 1.0 X 10(7), respectively. A linear increase in the specific radioactivity of L and H chain subunits was observed with increasing concentrations of 3H- or 14C-labeled formaldehyde in the reaction mixture and with increasing concentrations of L or H chain in the reaction mixture.

Structure of heavy and light chain subunits of type A botulinum neurotoxin analyzed by circular dichroism and fluorescence measurements

The secondary and tertiary structural features of botulinum neurotoxin (NT) serotype A, a dichain protein (Mr 145,000), and its two subunits, the heavy (H) and light (L) chains (Mr 97,000 and 53,000, respectively) were examined using circular dichroism and fluorescence spectorscopy. Nearly 70% of the amino acid residues in each of the three polypeptide preparations were found in ordered structure (sum of alpha helix, beta sheet and beta turns). Also, the alpha helix, beta sheet, beta turns and random coil contents of the dichain NT were nearly equal to the weighted mean of each of these secondary structure parameters of the L and H chains; e.g., sum of alpha helix of L chain (22%) and H chain (18.7%), as weighted mean, 19.8% was similar to that of NT (20%). These agreements suggested that the secondary structures of the subunits of the dichain NT do not significantly change when they are separated as isolated L and H chains. Fluorescence emission maximum of L chain, 4 nm less (blue shift) than that of H chain, suggested relatively more hydrophobic environment of fluorescent tryptophan residue(s) of L chain. Tryptophan fluorescence quantum yields of L chain, H chain and the NT, 0.072, 0.174 and 0.197, respectively, suggested that a) an alteration in the micro-environment of the tryptophan residues was possibly caused by interactions of L and H chain subunits of the NT and b) quantum yields for L and H chains were altered when they are together as subunits of the NT. Possible implications of structural features of the L and H chains, their interactions and the molecular mechanism of action of botulinum NT are assessed.

Reductive methylation of lysine residues of botulinum neurotoxin types A and B

Reductive methylation of botulinum neurotoxin (NT) serotypes A and B at various ratios of protein to reagent modified up to 75% of the lysine residues. Amino acid analysis of the modified proteins (HCl hydrolysed) confirmed selective modifications of lysine. The derivative N,N-dimethyl lysine was more abundant than monomethyl lysine; trimethyl lysine was not detected. Distribution of modified lysine residues among the heavy and light chains (Mr approximately 100,000 and approximately 50,000, respectively) of the dichain type A NT (Mr approximately 150,000) was approximately proportional to the lysine contents of the two subunit chains of the NT. Toxicity (mouse lethality) and serological reactivity (polyclonal antibody) of serotype A NT were not (or insignificantly) damaged following methylation of up to 72 lysine residues. Modification of 3 additional residues caused precipitous loss in toxicity. Toxicity of serotype B NT, unlike type A, appeared more sensitive to lysine modification. The large number of lysine residues that can be methylated without damaging toxicity of type A NT can be exploited to a) radiolabel the dichain protein exclusively in one chain keeping the other chain unlabelled, b) restrict the number of tryptic cleavage sites of the NT, and c) tag the protein with various markers or reactive ligands.

Clostridium botulinum toxins: nature and preparation for clinical use

C. botulinum neurotoxins are acutely toxic materials and act by inhibiting release of the neurotransmitter acetylcholine. The specific nature of this inhibition is discussed and the preparation and purification of Type A toxin specifically for clinical use is described.

Antigenic structure of Clostridium botulinum type B neurotoxin and its interaction with gangliosides, cerebroside, and free fatty acids

A fragment distinct from the heavy and light chains was obtained by treatment of Clostridium botulinum type B neurotoxin with chymotrypsin. Enzyme-linked immunosorbent assay and immunoblotting analysis with monoclonal antibodies showed that the fragment consisted of the light chain and part of the heavy chain (H-1 fragment) linked together by a disulfide bond. Monoclonal antibodies reacting to the heavy chain but not to the fragment were thought to recognize the epitopes on the remaining portion (H-2 fragment) of the heavy chain, being easily digested by chymotrypsin. Thus, the antigenic structure of type B neurotoxin resembles those of type A and E neurotoxins. The chymotrypsin-induced fragment bound to cerebroside and free fatty acids but not to gangliosides. The manner of binding of type B neurotoxin to gangliosides and free fatty acids was different from those of type A and E neurotoxins. Such differences in the reactivities to lipids may be related to the finding that each neurotoxin binds to a type-specific site on the neural membrane.

The use of monoclonal antibodies to analyze the structure of Clostridium botulinum type E derivative toxin

Six monoclonal antibodies against Clostridium botulinum type E derivative toxin were prepared. Three of the five binding to the heavy chain neutralized the derivative toxin; the other one binding to the light chain did not. Immunoblotting analysis with the monoclonal antibodies showed that the fragment obtained by tryptic digestion consisted of the light chain and part of the heavy chain (H-1 fragment) linked together by a disulfide bond(s) and that the antigenic determinants common between type E and F derivative toxins were located on both the heavy and light chains. The fragment induced by chymotrypsin treatment, like the tryptic fragment, bound to four monoclonal antibodies. The mild tryptic treatment and reduction resulted in separation of the chymotryptic fragment into two smaller fragments corresponding to the light chain and H-1 fragment. These results indicate that H-1 fragment contains the amino-terminal portion of the heavy chain. The monoclonal antibody neutralizing the toxin and probably recognizing the epitope on the carboxyl-terminal portion (H-2 fragment) of the heavy chain effectively competed for binding of 125I-labeled derivative toxin to synaptosomes. Of the two monoclonal antibodies neutralizing the toxin and recognizing the epitopes on H-1 fragment, one partially inhibited binding, but the other did not. This suggests that the binding of 125I-labeled derivative toxin depends mainly on the carboxyl-terminal region of the heavy chain and that interference with binding is not the only means of toxin neutralization.

Interaction of botulinum type A, B and E derivative toxins with synaptosomes of rat brain

Clostridium botulimum 125I-labelled derivative toxin immediately bound to rat synaptosomes. Of the two fragments of type B derivative toxin, the large-molecular-weight fragment (fragment I) inhibited the binding of labelled type B derivative toxin to synaptosomes in the same manner as unlabelled type B toxin did. The inhibition by the small-molecular-weight fragment (fragment II) was less than that by fragment I. These findings suggest that type B toxin binds to synaptosomes mainly with some part of fragment I. The binding of labelled type A and E derivative toxins was inhibited by either of the unlabelled type A or E derivative toxins, but not by type B derivative toxin. It is concluded that synaptosomes of rat brain possess relatively specific binding sites for botulinum toxin types.