Similarities in the heavy and light chains of tetanus toxin suggested by their amino acid compositions

Properties and use of botulinum toxin and other microbial neurotoxins in medicine

Crystalline botulinum toxin type A was licensed in December 1989 by the Food and Drug Administration for treatment of certain spasmodic muscle disorders following 10 or more years of experimental treatment on human volunteers. Botulinum toxin exerts its action on a muscle indirectly by blocking the release of the neurotransmitter acetylcholine at the nerve ending, resulting in reduced muscle activity or paralysis. The injection of only nanogram quantities (1 ng = 30 mouse 50% lethal doses [U]) of the toxin into a spastic muscle is required to bring about the desired muscle control. The type A toxin produced in anaerobic culture and purified in crystalline form has a specific toxicity in mice of 3 x 10(7) U/mg. The crystalline toxin is a high-molecular-weight protein of 900,000 Mr and is composed of two molecules of neurotoxin (ca. 150,000 Mr) noncovalently bound to nontoxic proteins that play an important role in the stability of the toxic unit and its effective toxicity. Because the toxin is administered by injection directly into neuromuscular tissue, the methods of culturing and purification are vital. Its chemical, physical, and biological properties as applied to its use in medicine are described. Dilution and drying of the toxin for dispensing causes some detoxification, and the mouse assay is the only means of evaluation for human treatment. Other microbial neurotoxins may have uses in medicine; these include serotypes of botulinum toxins and tetanus toxin. Certain neurotoxins produced by dinoflagellates, including saxitoxin and tetrodotoxin, cause muscle paralysis through their effect on the action potential at the voltage-gated sodium channel. Saxitoxin used with anaesthetics lengthens the effect of the anaesthetic and may enhance the effectiveness of other medical drugs. Combining toxins with drugs could increase their effectiveness in treatment of human disease.

Defining a region on tetanus toxin responsible for neuromuscular blockade

Administering high doses of tetanus toxin to animals produces neuromuscular blockade. Previous studies, in which specific F(ab) antibody fragments were used to mask the 50,000 MW COOH-terminal portion of the heavy chain (fragment c) on the toxin molecule, have shown that the paralyzing effect of the toxin was most probably located in an area comprising the light chain and the 50,000 MW NH2-terminal portion of the heavy chain (Fragment Ibc). In our study, the toxin was also complexed with F(ab) fragments directed to the light chain (alpha), heavy chain (beta), beta minus IIc, and with monoclonal antibodies to epitopes on IIc and beta minus IIc. Investigating the effect of the resulting complexes both in mice and on the sphincter pupillae muscle in rabbits permitted us to circumscribe further the tetanus toxin neuromuscular blocking activity in a region of the NH2-terminal fragment (Mr = 50,000) of the heavy chain (fragment beta minus IIc). Our results are consistent with the assumption that the beta minus IIc fragment is critical for the neuromuscular blockade activity of tetanus toxin. However, it cannot be ruled out that both the peripheral and central effects of the toxin result from the same portion of the toxin molecule, the nature of the action depending on where the toxin is carried after its introduction into the organism.

Human T4+ T-lymphocyte clones specific for the B fragment of tetanus toxin

Two T4+ cloned T-lymphocyte lines specific for a papain digest product of tetanus toxin are functionally characterized. The two clones were obtained from peripheral blood mononuclear cells activated in vitro by tetanus toxoid, expanded with IL-2, and cloned in soft agar. Both clones could be induced to undergo blastogenesis with tetanus toxoid, tetanus toxin, and the B fragment but not the C fragment of tetanus toxin. In addition, both clones caused cytolysis of plastic adherent cell targets cocultured for 18 hr with either tetanus or the B fragment. Antigen specific proliferation and cytolytic activity were MHC-class I restricted.

Antibodies against the light chain of tetanus toxin in human sera

Tetanus toxoid elicits protective antibodies against tetanus toxin in humans and animals. It has been reported that antitoxin from immunized humans contains no anti-light chain antibodies, based on immunodiffusion and quantitative precipitin analyses. We confirmed the absence of precipitating anti-light chain antibodies in tetanus immune globulin. However, the presence of antibodies against the light chain of the toxin was shown by direct binding and inhibition analyses, using enzyme-linked immunosorbent assays. Using a neutralization inhibition test, we also found that about one-fourth of the neutralizing antibodies in tetanus immune globulin are directed against the light chain. These results suggest that the light chain of tetanus toxin contains immunogenic determinants and that antibodies directed against it may have a role in the prevention of tetanus or treatment of tetanus or both.

Enzymatic hydrolysis of tetanus toxin by intrinsic and extrinsic proteases. Characterization of the fragments by monoclonal antibodies

Enzymatic fragments of tetanus toxin were characterized by immunoblotting using a set of previously characterized antibodies (Ahnert-Hilger et al. (1983) and a set of novel antibodies. The selected antibodies recognized the light chain, fragment C (beta 1), and the complementary piece (beta 2) of the heavy chain when blotted on nitrocellulose. All toxin preparations contained intrinsic esteroprotease activity which became manifest in the presence of urea. The main split product was a fragment (MW 100 000) reacting with anti-fragment C and anti-beta 2 antibodies. Toxicity does not depend on this protease activity. Some crude preparations of tetanus toxin contain another split product (MW 47 000) which resembles fragment C. The main product of papain hydrolysis is fragment C, which appears as a double band under nonreducing conditions but is homogeneous when reduced. Chymotryptic digestion hydrolyses the heavy chain well but leaves the light chain largely intact. Tetanus toxin is very resistant against trypsin as compared with other proteases, although this enzyme splits numerous different links. Our data show the usefulness of immunoblotting with monoclonal antibodies in analytical work with tetanus toxin, and the relevance of intrinsic proteases.

The amino acid compositions of proteins are correlated with their molecular sizes

Natural peptides and small proteins in general have amino acid compositions that diverge much more from the average composition of all proteins than do those of proteins. The effect is large and consistent enough to provide a rough check on the measured molecular mass of a protein and to indicate whether it is likely to have a significantly repetitive structure. For example, the alpha-chain of tropomyosin, a highly repetitive protein, has no amino acid composition that would be characteristic of a much smaller protein. The observation provides support for the suggestion [Taylor, Britton & van Heyningen (1983) Biochem. J. 209, 897-899] that tetanus toxin resembles a trimer of the light chain produced by proteolysis.