Ernst Habermann

A post-docking role for synaptobrevin in synaptic vesicle fusion

We have used the squid giant synapse to determine the role of synaptobrevin, integral membrane proteins of small synaptic vesicles, in neurotransmitter release. The sequence of squid synaptobrevin, deduced by cDNA cloning, is 65%-68% identical to mammalian isoforms and includes the conserved cleavage site for tetanus and botulinum B toxins. Injection of either toxin into squid nerve terminals caused a slow, irreversible inhibition of release without affecting the Ca2+ signal which triggers release. Microinjection of a recombinant protein corresponding to the cytoplasmic domain of synaptobrevin produced a more rapid and reversible inhibition of release, whereas two smaller peptide fragments were without effect. Electron microscopy of tetanus-injected terminals revealed an increased number of both docked and undocked synaptic vesicles. These data indicate that synaptobrevin participates in neurotransmitter release at a step between vesicle docking and fusion.

Tetanus toxin: primary structure, expression in E. coli, and homology with botulinum toxins.

A pool of synthetic oligonucleotides was used to identify the gene encoding tetanus toxin on a 75‐kbp plasmid from a toxigenic non‐sporulating strain of Clostridium tetani. The nucleotide sequence contained a single open reading frame coding for 1315 amino acids corresponding to a polypeptide with a mol. wt of 150,700. In the mature toxin molecule, proline (2) and serine (458) formed the N termini of the 52,288 mol. wt light chain and the 98,300 mol. wt heavy chain, respectively. Cysteine (467) was involved in the disulfide linkage between the two subchains. The amino acid sequences of the tetanus toxin revealed striking homologies with the partial amino acid sequences of botulinum toxins A, B, and E, indicating that the neurotoxins from C. tetani and C. botulinum are derived from a common ancestral gene. Overlapping peptides together covering the entire tetanus toxin molecule were synthesized in Escherichia coli and identified by monoclonal antibodies. The promoter of the toxin gene was localized in a region extending 322 bp upstream from the ATG codon and was shown to be functional in E. coli.

Palytoxin acts through Na+, K+-ATPase

Palytoxin is the most potent animal toxin, with a unique structure. The authors group has searched for its mode of action with the following results: 1. Palytoxin (1 pM and less) causes a fast K+ outflow from erythrocytes; 2. Extracellular Ca2+ and borate, and intracellular ATP enhance, but ouabain potently inhibits the palytoxin effects; 3. Palytoxin increases the permeability for Na+ and K+ but not for Ca2+; 4. Palytoxin in comparatively high concentrations (100 nM and above) inhibits Na+,K+-ATPase; 5. Palytoxin can be radiolabeled with 125I. Its receptor is very similar to, but not identical to that of ouabain. A reaction scheme has been delineated which allows an explanation to be obtained for all the known actions of palytoxin. It centers on the hypothesis that palytoxin binds to Na+,K+-ATPase and converts the enzyme or its close vicinity into an open channel with the permselectivity measured on erythrocytes. Patch clamp data from myocytes were obtained in other laboratories. They prove the presence of the predicted palytoxin channel.

LEAD AND OTHER METALS CAN SUBSTITUTE FOR CA2+ IN CALMODULIN

AbstractWe have studied the interaction between some heavy metal ions, as compared with earth alkali ions, and calmodulin, a tissue protein which binds Ca2+ and mediates some of its effects.1.Calmodulin dependent phosphodiesterase was activated with Pb2+, Ca2+, Sr2+, Ba2+, and Cd2+ (EC50 about 0.8 μM). The maximal activation achieved decreases in the order given. Hg2+ Sn2+, Fe2+, Cu2+, Ni2+, Bi3+, and Sb3+ up to 20 μM did not activate.2.Pb2+ can replace Ca2+ with respect to the calmodulin-dependent phosphorylation of brain membranes. With high Pb2+ concentrations, phosphorylation was inhibited.3.Calmodulin binding to brain membranes was enhanced with concentrations below 10−4 M in the following order: Pb2+ ≧Ca2+ ∼ Sr2+ > Cd2+ > Mn2+ > Ba2+. In contrast Mg2+, Hg2+, Sn2+, Fe2+, Ni2+, Co2+, and Cu2+ triggered, if at all, a non-saturable binding of calmodulin.4.In the flow-dialysis, other ions competed with 45Ca2+ binding to calmodulin in the following order: Pb2+ ∼ Ca2+ > Mn2+, Ba2+, Cd2+, Sr2+. Thus among the ions investigated Pb2+ is a fully potent substitute for Ca2+ in every calmodulin-dependent reaction investigated. Cd2+ is always much less potent. The earth alkali ions Sr2+ and Ba2+ take an intermediate position. It remains to be shown whether calmodulin is merely a storage site for Pb2+, or whether the resulting functional changes play a role in Pb2+ poisoning.

Tetanus toxin and botulinum A toxin inhibit release and uptake of various transmitters, as studied with particulate preparations from rat brain and spinal cord

SummaryThe effects of tetanus toxin and botulinum A toxin on the uptake and evoked release of various neurotransmitters were studied using particles from rat forebrain, corpus striatum and spinal cord. 1.Uptake. Tetanus toxin partially inhibits the uptake of glycine and choline into spinal cord synaptosomes. The effect on glycine uptake becomes statistically significant after a lag period of 60\2-120 min. It is no longer present when the toxin is heated, antitoxin-treated or toxoided. The inhibition by botulinum A toxin of choline uptake into spinal cord synaptosomes is weak but measurable, that of glycine uptake is at the borderline of detection.The uptake of GABA into forebrain cortex synaptosomes is slightly inhibited by tetanus toxin but hardly by botulinum A toxin. The effects of tetanus toxin and botulinum A toxin on the uptake of noradrenaline into striatal synaptosomes are negligible.2.Release. Tetanus toxin inhibits the potassium (25 mM) evoked release of radioactivity from rat forebrain cortex particles preloaded with labelled neurotransmitters. The sensitivity decreases in the following order: Glycine > GABA \2> acetylcholine. The toxin also inhibits the release of radioactivity from striatal particles preloaded with labelled noradrenaline. It is always 10\2-50 times more potent on spinal cord than on brain particles. The sensitivity of the evoked release from the spinal cord decreases in the order glycine > GABA > acetylcholine > noradrenaline.The toxin is identical with the causative agent because toxin-antitoxin complexes, toxoid and heated toxin do not influence the release from particles preloaded with glycine (spinal cord), GABA (forebrain) and noradrenaline (striatum).Botulinum toxin resembles tetanus toxin by its ability to diminish the release of radioactivity from preloaded forebrain (acetylcholine > GABA), striatal (noradrenaline), or spinal cord (glycine) particles. The botulinum toxin effect on the striatum (noradrenaline) and on the spinal cord (glycine) is due to its neurotoxin content.The identity of the toxin and the causative agent has been established by preheating and preincubation with antitoxin.It is proposed that a) tetanus and, however to a much lesser degree, botulinum A toxin act in a basically similar manner on a process underlying the function of synapses in general, and b) the pronounced sensitivity of glycine and GABA release from spinal cord, together with the axonal ascent of tetanus toxin, may be crucial in the pathogenesis of tetanus.

Tetanus toxin blocks the neuromuscular transmission in vitro like botulinum A toxin.

Summary1.The blocking effect of tetanus toxin on the neuromuscular junction of the mouse phrenic nervehemidiaphragm preparation exposed to the toxin (0.05–20 μg/ml) in the organ bath was studied and compared with the action of botulinum A toxin.2.The time course of the paralysis of the diaphragm could be divided into a latent and a manifest period. Still during the latent period the effect of the toxin became progressively resistant to washing and, with some delay, to antitoxin.3.Between 25 and 41°C the time until paralysis strongly depended on temperature with Q10 of about 2.7.4.Procedures increasing the transmitter release shortened, and procedures depressing it prolonged the time until paralysis.5.4-Aminopyridine and guanidine temporarily restored the contraction of the partially paralyzed diaphragm, indicating the persistence of activatable calcium and acetylcholine pools. Raising the external Ca2+-concentration and application of the Ca-Ionophore A 23187 were ineffective in the doses applied.6.About 80 min after exposure to the toxin (10 μg/ml), the m.e.p.p. activity decreased by a factor of 30. Parallel to this, paralysis of nerve evoked muscle contraction developed.7.Neuraminidase treatment did not prevent tetanus toxin poisoning.8.The paralysis is produced by tetanus toxin itself and not by contaminants as shown by the parallel decrease of toxicity and paralysis following treatment with either antitoxin or brain homogenate, or by the use of spontaneously inactivated toxin.9.Tetanus toxin was compared with botulinum A toxin as to the shape of its dose-response curve, time course of paralysis, temporary reversal by 4-aminopyridine and behaviour against Ca-ionophore. In any case, both toxins were indistinguishable, albeit botulinum A neurotoxin was calculated to be about 2000 times more potent than tetanus toxin.

125I-labeled neurotoxin from clostridium botulinum A: Preparation, binding to synaptosomes and ascent to the spinal cord

Summary1.Labeling of crystalline botulinum A toxin has been done with 125I by aid of the chloramine T method. The neurotoxic component is well preserved, whereas the hemagglutinin undergoes physicochemical alterations. Neither with labeled nor with unlabeled toxin, hemagglutinating power parallels the main protein peak.2.Neurotoxin, homogeneous in gel filtration, is bound to synaptosomes from rat brain. Cold toxin competes with labeled toxin, and antitoxin or neuraminidase partially remove the bound neurotoxin.3.Upon intramuscular injection, some radioactivity is recovered in the respective parts of the spinal cord. Antitoxin prevents the ascent. The similarities between tetanus and botulinum A neurotoxins are stressed.

Tetanus Toxin and Botulinum A and C Neurotoxins Inhibit Noradrenaline Release from Cultured Mouse Brain

Abstract: Primary nerve cell cultures from the brainstem of embryonic mice take up [3H]noradrenaline. Release can be evoked by high K+ or sea anemone toxin II and depends on Ca2+. The cultures allow neurochemical studies on the long‐term actions of clostridial neurotoxins. Tetanus and botulinum A and C neurotoxins partially inhibit the absolute and fractional release evoked by high K+, as well as the fractional basal release. The detection limit for the toxins is below 5 pM. Total radioactivity is higher in the poisoned cultures, although the initial velocity of uptake is not measurably influenced by tetanus or botulinum A toxin. Pretreatment with neuraminidase prevents the effects of botulinum A toxin and diminishes those of botulinum C and tetanus toxins. Within 6 days, the cultures partially recover from tetanus toxin poisoning. Antitoxin prevents the actions of the toxin, but only slightly promotes recovery. The data indicate close pharmacological analogies between the clostridial neurotoxins.

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/1. 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.

The renal handling of polybasic drugs

SummaryUpon intravenous injection of 3H-gentamicin in rats, radioactivity in serum rapidly declined to 3% of total within 1 h. Kidneys accumulated a constant amount (14%) of the injected radioactivity between 2 and 6 h after injection.In mice, simultaneous or prior application of unlabeled gentamicin (10 mg/kg) diminished the renal concentration of 3H-gentamicin, and aprotinin (10 mg/kg) was able to compete with labeled aprotinin. Aprotinin did not diminish the renal accumulation of gentamicin and vice versa. However, since 10 mg/kg aprotinin raised also the plasma concentrations of both 3H-gentamicin and 125I-aprotinin, the evidences resulting from these experiments are limited.Mouse kidney cortex was processed for light and electron microscopic autoradiography at different times following i.v. injection of 3H-gentamicin. Gentamicin enters the apical part of proximal tubule cells. Initially, brush border and basement membrane labeling is prominent, whereas lysosomes appear as intense and prevalent stores 20 min or later after injection.Fractionation of 3H-gentamicin loaded kidneys showed a similar distribution pattern of radioactivity and the lysosomal marker β-galactosidase. The same was true when the crude lysosomal fraction was subjected to density gradient centrifugation, which corroborates the microscopical findings. Radioactivity is partially bound to lysosomal structures, for repeated freezing of loaded lysosomes left 35% of radioactivity particle-bound.It is concluded that both gentamicin and peptides are handled in a similar manner by adsorption, followed by endocytosis and lysosomal sequestration in proximal tubule cells.