Separation and characterization of heavy and light chains from Clostridium botulinum type C toxin and their reconstitution

Developement of serum-free media in CHO-DG44 cells using a central composite statistical design

A serum free medium was developed for the production of recombinant antibody against Botulinum A (BoNTA) using dihydrofolate reductase deficient Chinese Hamster Ovary Cells (CHO-DG44) in suspension culture. An initial control basal medium was prepared, which was similar in composition to HAM's F12: IMDM (1:1) supplemented with insulin, transeferrin, selenium and a lipid mixture. The vitamin concentration of the basal medium was twice that of HAM's F12: IMDM (1:1). CHO-DG44 cells expressing S25 antibody grew from 2 x 10(5) cells to maximum cell density of 1.04 x 10(6) cells/ml after 5 days in this control medium. A central composite design was used to identify optimal levels and interaction among five groups of medium components. These five groups were glutamine, Essential Amino Acids (EAA), Non Essential Amino Acids (NEAA), Insulin, Transferrin, Selenium (ITS), and lipids. Fifty experiments were carried out in four batches, with two controls in each batch. There was little effect of ITS and Lipid concentrations over the range studied, and glutamine concentration showed a strong interaction with EAA. The optimal concentrations of the variables studied were 2.5 mM Glutamine, 7.4 mM (2x) EAA, 1.4 mM (0.5x) NEAA, 1x ITS supplement, 0.7x Lipids supplement. The maximum viable cell density attained in the optimized medium was 1.4 x 10(6) cells/ml, a 35% improvement over the control culture, while the final antibody titer attained was 22 +/- 3.4 mug/mL, a 50% improvement.

A highly sensitive immuno-polymerase chain reaction assay for Clostridium botulinum neurotoxin type A

Our goal was to develop a sensitive method for detecting Clostridium botulinum neurotoxin type A (BoNT/A). We were able to detect BoNT/A in the femtogram (10(-15)g) range using an indirect immuno-polymerase chain reaction (immuno-PCR) assay and an indirect sandwich immuno-PCR assay. For the indirect immuno-PCR assay, enzyme-linked immunosorbent assay (ELISA) plates were coated with BoNT/A that was recognized by anti-BoNT/A monoclonal antibody. For the indirect sandwich immuno-PCR assay, the monoclonal antibody was immobilized on ELISA plates for detecting BoNT/A that was recognized by its polyclonal antibodies. Reporter DNA was prepared by PCR amplification using biotinylated 5'-primers, and it was coupled with biotinylated antibodies through streptavidin. In order to increase sensitivity and reduce background noise, the amounts of reporter DNA (ranging from 50 fg to 50 ng) and streptavidin (ranging from 0.125 ng to 8 ng) were optimized. Using the optimized concentration of reporter DNA and streptavidin, both indirect and indirect sandwich immuno-PCR assays detected BoNT/A as low as 50 fg. These results are a 10(5)-fold improvement over conventional indirect ELISA and indirect sandwich ELISA methods. The assays we developed are currently the most sensitive methods for detecting BoNT/A.

Characterization of neutralizing antibodies and identification of neutralizing epitope mimics on the Clostridium botulinum neurotoxin type A

Clostridium botulinum neurotoxin type A (BTx-A) is known to inhibit the release of acetylcholine at the neuromuscular junctions and synapses and to cause neuroparalysis and death. In this study, we have identified two monoclonal antibodies, BT57-1 and BT150-3, which protect ICR mice against lethal doses of BTx-A challenge. The neutralizing activities for BT57-1 and BT150-3 were 10(3) and 10(4) times the 50% lethal dose, respectively. Using immunoblotting analysis, BT57-1 was recognized as a light chain and BT150-3 was recognized as a heavy chain of BTx-A. Also, applying the phage display method, we investigated the antibodies' neutralizing B-cell epitopes. These immunopositive phage clones displayed consensus motifs, Asp-Pro-Leu for BT57-1 and Cys-X-Asp-Cys for BT150. The synthetic peptide P4M (KGTFDPLQEPRT) corresponded to the phage-displayed peptide selected by BT57-1 and was able to bind the antibodies specifically. This peptide was also shown by competitive inhibition assay to be able to inhibit phage clone binding to BT57-1. Aspartic acid (D(5)) in P4M was crucial to the binding of P4M to BT57-1, since its binding activity dramatically decreased when it was changed to lysine (K(5)). Finally, immunizing mice with the selected phage clones elicited a specific humoral response against BTx-A. These results suggest that phage-displayed random-peptide libraries are useful in identifying the neutralizing epitopes of monoclonal antibodies. In the future, the identification of the neutralizing epitopes of BTx-A may provide important information for the identification of the BTx-A receptor and the design of a BTx-A vaccine.

Binding of botulinum type Cl, D and E neurotoxins to neuronal cell lines and synaptosomes

Clostridium botulinum 125I-labeled Cl neurotoxin bound to NG108 hybridoma cell line. Unlabeled type Cl neurotoxin inhibited the binding of the labeled Cl toxin but neither types D nor E toxin. 125I-labeled type D neurotoxin bound to rat brain synaptosomes but did not bind to NG108 cells. It is suggested that receptors for types C and D or E toxins on neuronal cell membranes are different.

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.

Binding of Clostridium botulinum type C neurotoxin to different neuroblastoma cell lines

Binding of type C neurotoxin (C1 toxin) from Clostridium botulinum (strain Stockholm) to neuroblastoma cell lines was studied by using biotinylated anti-toxin antibody and avidin-biotinylated peroxidase complex. The neurotoxin bound with high efficiency to mouse neuroblastoma (NS-20Y and NIE-115) cells and to hybridomas of rat glioblastoma and mouse neuroblastoma (NG108-C15) cells. The toxin bound little to human neuroblastoma, rat astrocytoma, and nonneural cell lines. Binding of the neurotoxin to NG108-C15 cells was inhibited by gangliosides (GT1b and GM1) and by monoclonal antibodies (CA-12 and C-9), although inhibition was not complete. Sequential preincubation of C1 toxin with GT1b and CA-12 caused complete inhibition. A Scatchard plot of binding of 125I-labeled C1 toxin to NG108-C15 cells showed a hyperbolic curve. Monoclonal antibody CA-12 but not C-9 neutralized the lethal activity of the toxin toward mice. Only C-9 clearly inhibited toxin binding to GT1b. These results suggest that NG108-C15 cells have at least two kinds of receptors for C1 toxin. From the results of binding tests with neuraminidase-, pronase-, and trypsin-treated NG108-C15 cells, the chemical nature of the high-affinity site was presumed to be a glycoprotein containing sialic acid. GT1b may have an important role in low-affinity sites.

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.

Rapid method for purification of Clostridium botulinuh type C neurotoxin by High Performance Liquid Chromatography (HPLC )

The culture supernatant of Clostridium botulinum type C, concentrated by addition of RNA, acid precipitation and subsequent protamine treatment was used as starting material for rapid purification of L toxin (mol. wt. ca. 500K) and M toxin (mol. wt. ca. 350K) of C1 neurotoxin by ion-exchange chromatography on a Mono S column by fast performance liquid chromatography (FPLC). L and M toxins were highly purified further by gel permeation chromatography through a TSK G3000SW column at pH 6.0 by high performance liquid chromatography (HPLC). Purified S toxin (mol. wt. ca. 150K, Cl neurotoxin without a nontoxic component) was then obtained from L toxin rapidly by gel permeation chromatography at pH 7.3 through a TSK G3000SW column by HPLC. Purified S toxin was also obtained rapidly from M and L toxins by ion-exchange chromatography on a Mono Q column at pH 8.0 using an FPLC system. The purified preparations of L, M and S toxins gave single bands on conventional polyacrylamide gel electrophoresis, and had specific activities of 2.8, 6.7, and 14-21 × 10⁷ LD₅₀/mg N, respectively, in mice. On immunoelectrophoresis, purified S toxin gave a single arc against anti-crude toxin serum. The yield of toxicity as L and M toxins was 73.1% (32.5% as L toxin and 40.6% as M toxin) from the protamine-treated concentrated culture supernatant. The recovery of toxicity as S toxin from purified L or M toxin was almost 100% (97.6-100% of L toxin and 97.5% of M toxin). These procedures provide a rapid method for purifying L and M toxins, which have stable toxicities. The method will also be very useful for rapid preparation of the toxic component (S toxin) of C1 neurotoxin, which is unstable, in small amounts from the L and M toxins just before its use in experiments.

Evidence for direct binding of Clostridium botulinum type E derivative toxin and its fragments to gangliosides and free fatty acids

Clostridium botulinum type E derivative toxin and its heavy chain bound to gangliosides GT1b, GD1a and GQ1b and saturated and unsaturated free fatty acids with chain lengths of 14-20 carbons. The L-H-1 fragment lacking the carboxyl-terminal portion of the heavy chain bound to free fatty acids but not to gangliosides. These observations led us to a new hypothesis on the mechanism of binding between botulinum toxin and gangliosides; the carboxyl-terminal portion (H-2 fragment) of the heavy chain binds to an oligosaccharide residue of gangliosides and then the amino-terminal portion (H-1 fragment) interacts with the hydrophobic portion of gangliosides consisting of fatty acids.

Botulinum neurotoxin type B. Its purification, radioiodination and interaction with rat-brain synaptosomal membranes

Neurotoxin from Clostridium botulinum type B was purified to homogeneity by by affinity and ion-exchange chromatography; specific neurotoxicity of this protein (Mr of approximately equal to 155 000) following trypsinisation attained a level of 2 X 10(8) mouse LD50 units/mg protein. 125I-iodination of the toxin to high specific radioactivities (19-63 TBq/mmol) yielded typically greater than 65% of its original toxicity; dodecyl sulphate gel electrophoresis under reducing conditions, after trypsinisation, showed that the larger polypeptide (Mr of approximately equal to 101 000) was labelled preferentially. Saturable binding of the 125I-labelled neurotoxin to rat cerebrocortical synaptosomes was observed and Scatchard analysis showed a low content of acceptors with high affinity (Kd = 0.3-0.5 nM;Bmax approximately equal to 30-60 fmol/mg protein, together with a much larger population of weak-affinity sites. No significant differences in binding affinity were seen in competition experiments using native or fully activated (trypsinized) neurotoxin, indicating that chain cleavage is not essential for acceptor-toxin interaction. Type A botulinum neurotoxin showed a limited capacity to inhibit the synaptosomal binding of labelled type B toxin, even at high concentrations (1 muM), and other neurotoxins were without effect, emphasising the acceptor selectivity. Near-complete loss of specific toxin binding was produced by preincubation of synaptosomes with neuraminidase whereas inhibition of the low-affinity sites with wheat-germ agglutinin was less pronounced; such inactivation was prevented by inclusion of selective inhibitors (2,3-dehydro-2-deoxy-N-acetylneuraminic acid and N-acetylglucosamine, respectively). These observations implicate N-acetylneuraminic acid and, possibly, other sugar moieties as constituents of the toxin acceptors. Trypsinisation of synaptosomes gave incomplete inhibition of binding when assayed with 1 nM or 10 nM 125I-iodinated toxin. Detailed analysis of the actions of neuraminidase, trypsin and heat treatment on the concentration dependence of toxin binding suggest the existence of at least two distinguishable populations of sites that contain N-acetylneuraminic acid, with a protein component being associated with the acceptors of lower affinity. These findings are discussed in relation to those previously reported for type A neurotoxin and to the possible physiological significance of such membrane acceptors.

Partial amino acid sequences of botulinum neurotoxins types B and E

Clostridium botulinum type E neurotoxin, a single-chain protein of Mr 147,000, was purified and subjected to amino acid sequencing. The same was done for single-chain botulinum type B neurotoxin (Mr 152,000), and for the heavy and light chains (Mr 104,000 and 51,000 respectively) derived from type B by limited trypsin digestion. Twelve to eighteen residues were identified and the following conclusions were drawn: The light chain of the nicked (dichain) type B is derived from the N-terminal one-third of the single-chain (unnicked) parent neurotoxin; sequence homologies are present between single-chain types B and E and the light chain of the nicked type A [J. J. Schmidt, V. Sathyamoorthy, and B. R. DasGupta (1984) Biochem. Biophys. Res. Commun. 119, 900-904]; the N-terminal regions of the heavy chains of types A and B have some structural similarity; and activation of type B neurotoxin cannot involve removal of amino acids or peptides from the N terminus.

Partial amino acid sequences of the heavy and light chains of botulinum neurotoxin type E

The dichain type E botulinum neurotoxin, a product of nicking the single chain protein by trypsin, is composed of a heavy and light chains. Sequence of the first 13 and 20 N-terminal residues of these two chains were determined. Also, proof is provided here that (i) the light chain of the nicked (dichain) is derived from the N-terminal one-third of the parent single chain neurotoxin, and (ii) molecular events leading to the activation, of the single chain neurotoxin cannot involve tryptic cleavage at or very close to the N-terminal of the single chain protein. The partial amino acid sequence of the light chain of botulinum type E and tetanus neurotoxins show significant similarity between the two clostridial neurotoxins.

Comparison of Clostridium botulinum toxins type D and C1 in molecular property, antigenicity and binding ability to rat-brain synaptosomes

Botulinum type D neurotoxin was purified 950-fold from the culture supernatant with an overall yield of 32%. The purified toxin had a specific toxicity of 5.8 X 10(7) mouse minimal lethal dose per mg of protein and a relative molecular mass of 140000. The purified toxin had a di-chain structure consisting of heavy and light chains with relative molecular masses of 85000 and 55000, respectively, linked by one disulfide bond. These subunits had different amino acid compositions and antigenicities. A similarity in molecular constructions and amino acid compositions was observed between type D and type C1 toxins as well as between their subunits. Among the seven kinds of monoclonal antibodies against type D toxin, six reacted with the heavy chain of type D toxin, while one of the six also reacted with the heavy chain of type C1 toxin and neutralized the toxicities of the two toxins. The other one of monoclonal antibodies reacted with the light chains of both toxins. This evidence indicates that both toxins have common antigenic sites on their heavy and light chains and that the antigenic site on the heavy chain may contribute to the neutralization of both toxins by antibody. The binding of type D toxin to rat brain synaptosomes was examined by use of 125I-labelled type D toxin. The binding was competitively inhibited not only by unlabelled type D and C1 toxins, but also by the heavy chains of both toxins, however, it was not inhibited by the light chain of type D toxin. These results suggest that the toxin receptors on synaptosomal membrane are common for type D and C1 toxins, and that the heavy chain contributes to the binding of toxin to synaptosomes and the structure of the binding sites on the heavy chains of both toxins is quite similar.

Purification and amino acid composition of type A botulinum neurotoxin

A method to purify type A botulinum neurotoxin from a 64 liter bacterial culture is reported. The procedure includes cation exchange chromatography at pH 7.0. The final product, essentially homogeneous (according to polyacrylamide gel-sodium dodecylsulfate electrophoresis), is a mixture of two forms of the neurotoxin (mol. wt 145,000); the dichain or nicked form (over 95%) and its precursor the single chain or unnicked form. Two batches of the neurotoxin purified by the method described here and one batch purified according to the method of Sugii and Sakaguchi were similar in purity and amino acid composition. The best estimate of the number of amino acid residues per neurotoxin molecule (mol. wt 145,000) is: Asp200Thr75Ser79Glu114Pro44Gly64Ala53Val70CyS10Met22Ile111Leu104Tyr71 Phe68Lys100His14Arg43Trp17.

Amino acid composition of Clostridium botulinum type F neurotoxin

To develop reliable data on the amino acid composition of type F botulinum neurotoxin, three batches of the neurotoxin were analyzed. Each batch was isolated from a separate neurotoxin producing bacterial culture. Two batches had inoculum from one source and the other batch one from a different source. Two batches of the neurotoxin were purified by the same method and one was purified by a different method. The neurotoxin preparations were found comparable in purity and similar in amino acid composition. The best estimate of number of amino acid residues per neurotoxin molecule (mol. wt. 155,000) was: Asp218 Thr80 Ser105 Glu128 Pro47 Gly69 Ala47 Val72 CyS9 Met14 Ile128 Leu104 Tyr86 Phe60 Lys90 His13 Arg51 Trp23.

Clostridium botulinum type C toxin: a sketch of the molecule

The purification and crystallization of type C botulinum toxin along with its physical characteristics are described. The shape of Clostridium botulinum type C toxin molecule is globular like a pressed ball with a 7.4 nm diameter and a 4.3 nm thickness. The molecular volume is approximately 185 nl and the molecular weight is 141000. The toxin molecule is composed of two parts, which are separable under appropriate conditions. These parts have some differences in the electrophoretic properties, amino acid distribution, immunological, and functional characteristics. The toxin molecule can be reconstituted by association of S-S bond between the two chains. The expression of the toxicity requires that the fragments of the polypeptide chain carrying the necessary information be functionally organized for the proper development of the specific tertiary structure for active conformation.