Enzymatic breakdown of tetanus toxin

Treatment of tetanus toxin with papain at 55°C resulted in breakdown of the molecule to yield an atoxic fraction with a molecular weight of approximately 40 000. The highly purified material exhibited partial immunological identity with the parent toxin, showed no toxicity and elicited the formation of neutralizing antibodies against tetanus.     

Action of botulinum A toxin and tetanus toxin on synaptic transmission

Intracellular recordings of the spontaneous activity from mammalian spinal cord neurons in culture demonstrated different sensitivities of excitatory and inhibitory synaptic transmission for the action of tetanus toxin (Tetx) and botulinum toxin type A (Botx). The effects of Tetx and Botx on spontaneous and nerve-evoked transmitter release were compared under identical experimental conditions in experiments on in vitro poisoned mouse diaphragms. At 37 degrees C completely paralyzed endplates are characterized by a very low frequency of spontaneous miniature endplate potentials (m.e.p.p.s) and by a 100% failure to evoke endplate potentials (e.p.p.s) in response to single nerve stimuli. Striking differences in the action of both toxins have been observed when the very low transmitter release probabilities of paralyzed nerve-muscle preparations were increased by tetanic nerve stimulation and/or application of potent K+-channel blockers and/or by reduction of temperature to 25 degrees C. While Botx did not change the short latency between nerve impulse and postsynaptic response, Tetx produced a temporal dispersion of the quantal release suggesting that the toxins act at different sites in the chain of events that result in transmitter release. To find further evidence to support the different actions of the toxins the spontaneous transmitter release was studied in more detail. Tetx blocked preferentially the release of so-called large mode m.e.p.p.s without affecting the frequency of the small mode ones. In contrast, Botx strongly inhibited both the small and large mode m.e.p.p.s.(ABSTRACT TRUNCATED AT 250 WORDS)     

The tetanus toxin light chain inhibits exocytosis

The intracellular action on exocytosis of various forms of tetanus toxin was studied using adrenal medullary chromaffin cells, the membrane barrier of which has been removed by permeabilization with streptolysin O. Such cells still release catecholamines on stimulation with calcium. The two-chain form of tetanus toxin (67 nmol/l) strongly inhibited exocytosis, but only if dithiothreitol was present as a reducing agent. Purified light chain completely prevented [3H]noradrenaline release with a half-maximal effect at about 5 nmol/l. Heavy chain (up to 11 nmol/l) and unprocessed single-chain toxin (up to 133 nmol/l) were without effect. It is concluded that the original single-chain form of tetanus toxin has to be processed by proteolysis and reduction to yield a light chain which inhibits transmitter release.     

Serotonin transporter phosphorylation modulated by tetanus toxin

Tetanus toxin (TeTx) modifies Na(+)-dependent, high-affinity 5-hydroxytryptamine (5-HT, serotonin) uptake in a synaptosomal-enriched P(2) fraction from rat brain. The effect corresponds to a rapid and non-competitive uptake inhibition, and it is preceded by induction of phospholipase C (PLC) activity and translocation and down-regulation of the classical protein kinase C (PKC-alpha, -beta and -gamma) isoforms. The effects on serotonin transport and on cPKC activation were similar to the effects exhibited by phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). Moreover, after treatment with TeTx, an increase in Ser- and Tyr-specific phosphorylation was found. Activation of PKC by both TeTx and TPA results in a loss of transport capacity and serotonin transporter (SERT) phosphorylation, which are abolished by coapplication of the specific PKC inhibitor bisindolylmaleimide-1. Since a specific PLCgamma1 phosphorylation prior to TeTx's inducing SERT phosphorylation was found, the studies suggest that part of the action of TeTx consists of modifying the signal cascade initiated in tyrosine kinase receptors on nerve tissue previous to its cellular internalization, resulting in transporter phosphorylation.     

Molecular basis for tetanus toxin coreceptor interactions

Tetanus toxin (TeNT) elicits spastic paralysis through the cleavage of vesicle-associated membrane protein-2 (VAMP-2) in neurons at the interneuronal junction of the central nervous system. While TeNT retrograde traffics from peripheral nerve endings to the interneuronal junction, there is limited understanding of the neuronal receptors utilized by tetanus toxin for the initial entry into nerve cells. Earlier studies implicated a coreceptor for tetanus toxin entry into neurons: a ganglioside binding pocket and a sialic acid binding pocket and that GT1b bound to each pocket. In this study, a solid phase assay characterized the ganglioside binding specificity and functional properties of both carbohydrate binding pockets of TeNT. The ganglioside binding pocket recognized the ganglioside sugar backbone, Gal-GalNAc, independent of sialic acid-(5) and sialic acid-(7) and GM1a was an optimal substrate for this pocket, while the sialic acid binding pocket recognized sialic acid-(5) and sialic acid-(7) with "b"series of gangliosides preferred relative to "a" series gangliosides. The high-affinity binding of gangliosides to TeNT HCR required functional ganglioside and sialic acid binding pockets, supporting synergistic binding to coreceptors. This analysis provides a model for how tetanus toxin utilizes coreceptors for high-affinity binding to neurons.