Increase of permeability of synaptosomes and liposomes by the heavy chain of tetanus toxin

Recombinant forms of tetanus toxin engineered for examining and exploiting neuronal trafficking pathways

Tetanus toxin is a fascinating, multifunctional protein that binds to peripheral neurons, undergoes retrograde transport and trans-synaptic transfer to central inhibitory neurons where it blocks transmitter release, thereby, causing spastic paralysis. As a pre-requisite for exploiting its unique trafficking properties, a novel recombinant single chain was expressed at a high level in Escherichia coli as a soluble, easily purifiable protein. It could be activated with enterokinase to produce a dichain that matched native toxin in terms of proteolytic and neuroinhibitory activities, as well as induction of spastic paralysis in mice. Importantly, nicking was not essential for protease activity. Substitution of Glu(234) by Ala created a protease-deficient atoxic form, which blocked the neuroparalytic action of tetanus toxin in vitro, with equal potency to its heavy chain; but, the mutant proved >30-fold more potent in preventing tetanus in mice. This observation unveils differences between the intoxication processes resulting from retrograde transport of toxin in vivo and its local uptake into peripheral or central nerves in vitro, dispelling a popularly held belief that the heavy chain is the sole determinant for efficient trafficking. Thus, this innocuous mutant may be a useful vehicle, superior to the heavy chain, for drug delivery to central neurons.

Gating and permeability of ion channels produced by botulinum toxin types A and E in PC12 cell membranes

Botulinum neurotoxin (BoNT) is known to produce cationic channels in artificial bilayers. This study examined ion channels formed by BoNT in native membranes from cultured PC12 cells under conditions approximating those thought to occur during toxin internalization. Membrane patches were excised from PC12 cells using patch electrodes and exposed to symmetrical solutions containing either 200 mM CsCl, RbCl or KCl. The patch pipettes also contained 1-5 microg/ml BoNT buffered to pH 5.3 while the bath solutions were buffered to pH 7.0. In the presence of toxin, bursts of ion channel openings were observed. These toxin-induced channels were most active with a negative voltage applied to the same side as the toxin (cis). The increased activity at negative voltages was due to an increase in mean open time of e-fold per 120 mV and a decrease in mean closed time between bursts of e-fold per 110 mV. The shorter mean closed time within a burst was independent of membrane voltage. While BoNT-induced ion channels started as a single conductance level of 27 pS (KCl), 34 pS (RbCl) or 46 pS (CsCl) they typically increased in roughly equal steps to five or more times the original channel conductance. These higher conductance BoNT 'channels' opened and closed synchronously and could be distinguished from superposition of multiple independent channels. Despite differences in putative transmembrane sequences between BoNT/A and BoNT/E, both serotypes evidenced the same channel conductance and mean open time.

Synaptobrevin cleavage by the tetanus toxin light chain is linked to the inhibition of exocytosis in chromaffin cells

Exocytosis of secretory granules by adrenal chromaffin cells is blocked by the tetanus toxin light chain in a zinc specific manner. Here we show that cellular synaptobrevin is almost completely degraded by the tetanus toxin light chain within 15 min. We used highly purified adrenal secretory granules to show that synaptobrevin, which can be cleaved by the tetanus toxin light chain, is localized in the vesicular membrane. Proteolysis of synaptobrevin in cells and in secretory granules is reversibly inhibited by the zinc chelating agent dipicolinic acid. Moreover, cleavage of synaptobrevin present in secretory granules by the tetanus toxin light chain is blocked by the zinc peptidase inhibitor captopril and by synaptobrevin derived peptides. Our data indicate that the tetanus toxin light chain acts as a zinc dependent protease that cleaves synaptobrevin of secretory granules, an essential component of the exocytosis machinery in adrenal chromaffin cells.

Quaternary structure of botulinum and tetanus neurotoxins as probed by chemical cross-linking and native gel electrophoresis

Botulinum and tetanus neurotoxins are water-soluble proteins (mol. wt 150,000) produced by Clostridium botulinum and Clostridium tetani, respectively. It is believed that these neurotoxins, once internalized via receptor-mediated endocytosis, form membrane channels in order to traverse the endosomal membrane and enter the cytoplasm of the nerve terminal. Investigation of the associative properties between neurotoxin molecules could yield an understanding of this channel formation. That is, an association between neurotoxin monomers could result in an oligomeric form of the neurotoxin necessary for assembly of a channel through the hydrophobic interior of the endosomal membrane, thereby allowing passage of the neurotoxin or its active fragment through the resulting pore. Based on the native gel electrophoresis and chemical cross-linking experiments, tetanus neurotoxin exists as a dimer and a trimer, type A botulinum neurotoxin exists as a dimer, trimer, and a larger species, type E botulinum neurotoxin exists as a monomer and dimer, and type B botulinum neurotoxin appears to exist as a dimer in aqueous solution. The results imply that quaternary structures of these neurotoxins may play an important role in their mode of action during neuronal poisoning.

Pore formation by tetanus toxin, its chain and fragments in neuronal membranes and evaluation of the underlying motifs in the structure of the toxin molecule

The pore-forming activity of tetanus toxin, its chains and fragments was studied on membrane patches from spinal cord neurons of fetal mice using the outside-out patch-clamp configuration. 1. The dichain tetanus toxin forms pores at pH 5, but not at pH 7.4. The elementary pore conductance is 38.4 +/- 1.1 pS and nonselective for small cations. The open probability of the pores is voltage-dependent and increases with membrane depolarisation. The pores activate at +80 mV with a time constant of about 20 ms and deactivate at -80 mV with two time constants of about 2 ms and 10 ms. Besides the elementary pore conductance, larger pore conductances which are multiples of the elementary conductance were observed. With increasing conductances, their frequency of occurrence decreases exponentially. 2. The light chain of tetanus toxin alone does not form pores in neuronal membranes at pH 5 or at pH 7.4. 3. The heavy chain of tetanus toxin forms pores at pH 5 as well as at pH 7.4. The single pore conductance increases from 35.0 +/- 1.2 pS at pH 5 to 43.2 +/- 1.8 pS at pH 7.4. The pores allow mono- and divalent cations and chloride ions to pass. Only at pH 5 do they have a voltage dependence with time constants identical to those obtained with tetanus toxin. 4. Secondary structure predictions show a high density of presumably helically organized elements in fragment beta 2 (45 kDa) of the heavy chain between residues 700-850.(ABSTRACT TRUNCATED AT 250 WORDS)

Exploring the functional domain and the target of the tetanus toxin light chain in neurohypophysial terminals

The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial nerve terminals. Here we show that histidine residue 233 within the putative zinc binding motif of the tetanus toxin light chain is essential for the inhibition of exocytosis, in the rat. The zinc chelating agent dipicolinic acid as well as captopril, an inhibitor of zinc-dependent peptidases, counteract the effect of the neurotoxin. Synthetic peptides, the sequences of which correspond to motifs present in the cytoplasmic domain of the synaptic vesicle membrane protein synaptobrevin 1 and 2, prevent the effect of the tetanus toxin light chain. Our results indicate that zinc bound to the zinc binding motif constitutes the active site of the tetanus toxin light chain. Moreover they suggest that cleavage of synaptobrevin by the neurotoxin causes the inhibition of exocytotic release of vasopressin from secretory granules.

Functional characterization of the catalytic site of the tetanus toxin light chain using permeabilized adrenal chromaffin cells

The molecular events underlying the inhibition of exocytosis by tetanus toxin were investigated in permeabilized adrenal chromaffin cells. We found that replacement of amino acid residues within the putative zinc binding domain of the tetanus toxin light chain such as of histidine (position 233) by cysteine or valine, or of glutamate (position 234) by glutamine completely abolished the effect of the light chains on Ca2+ induced catecholamine release. Dipicolinic acid, a strong chelating agent for zinc, also prevented the effect of the tetanus toxin light chain. Zn2+ and, less potently Cu2+ and Ni2+, but not Cd2+ and Co2+, restored the activity of the neurotoxin. These data show that zinc and the putative zinc binding domain constitute the active site of the tetanus toxin light chain. Neither captopril, an inhibitor of synaptobrevin cleavage nor peptides spanning the site of synaptobrevins cleaved by the tetanus toxin in neurons, prevented the inhibition of Ca2+ induced catecholamine release by the tetanus toxin light chain. This suggests that synaptobrevins are not a major target of tetanus toxin in adrenal chromaffin cells.

Comparison of the intracellular effects of clostridial neurotoxins on exocytosis from streptolysin O-permeabilized rat pheochromocytoma (PC 12) and bovine adrenal chromaffin cells

The inhibitory effects of tetanus toxin, botulinum toxin A, their constituent light chains, and botulinum toxin B were compared using streptolysin O-permeabilized rat pheochromocytoma (PC 12) and bovine adrenal chromaffin cells in primary culture. In both types of chromaffin cells exocytosis can be triggered by micromolar amounts of free Ca2+, bovine adrenal chromaffin cells in addition require ATP. In PC 12 cells the isolated tetanus toxin light chain alone blocks exocytosis without any additive. The time-course of the inhibitory action of tetanus toxin light chain in permeabilized PC 12 cells in the absence of ATP is similar to the one obtained with permeabilized bovine adrenal chromaffin cells, in the presence of ATP. Thus, ATP does not seem to be crucial for tetanus toxin (two-chain form) poisoning. Botulinum toxin B (two-chain form), if preactivated by dithiothreitol, also inhibits exocytosis from permeabilized PC 12 cells up to 90% in the absence of ATP. By contrast, botulinum toxin A (two-chain form) or its isolated light chain, which are highly potent in permeabilized bovine adrenal chromaffin cells, causes only a weak inhibition in PC 12 cells. In streptolysin O-permeabilized bovine adrenal chromaffin cells omission of ATP during the incubation with the toxin increases the potency of botulinum toxin A light chain. Under the same conditions the effect of tetanus toxin light chain remains unchanged. Tetanus toxin and botulinum toxin B (two-chain forms) probably block a step which occurs during exocytosis from both PC 12 cells and adrenal chromaffin cells and which could be closely related to the final fusion event.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of phospholipids with proteins and peptides. New advances III

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins and peptides. 2. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecules is also discussed.