Bernard Poulain

Bio: Bernard Poulain is an academic researcher from University of Strasbourg. The author has contributed to research in topics: Neurotoxin & Synaptic vesicle. The author has an hindex of 36, co-authored 105 publications receiving 6106 citations. Previous affiliations of Bernard Poulain include Pasteur Institute & Centre national de la recherche scientifique.

Tetanus and botulinum-B neurotoxins block neurotransmitter release by proteolytic cleavage of synaptobrevin

Abstract: Clostridial neurotoxins, including tetanus toxin and the seven serotypes of botulinum toxin (A-G), are produced as single chains and cleaved to generate toxins with two chains joined by a single disulphide bond (Fig. 1). The heavy chain (M(r) 100,000 (100K)) is responsible for specific binding to neuronal cells and cell penetration of the light chain (50K), which blocks neurotransmitter release. Several lines of evidence have recently suggested that clostridial neurotoxins could be zinc endopeptidases. Here we show that tetanus and botulinum toxins serotype B are zinc endopeptidases, the activation of which requires reduction of the interchain disulphide bond. The protease activity is localized on the light chain and is specific for synaptobrevin, an integral membrane protein of small synaptic vesicles. The rat synaptobrevin-2 isoform is cleaved by both neurotoxins at the same single site, the peptide bond Gln 76-Phe 77, but the isoform synaptobrevin-1, which has a valine at the corresponding position, is not cleaved. The blocking of neurotransmitter release of Aplysia neurons injected with tetanus toxin or botulinum toxins serotype B is substantially delayed by peptides containing the synaptobrevin-2 cleavage site. These results indicate that tetanus and botulinum B neurotoxins block neurotransmitter release by cleaving synaptobrevin-2, a protein that, on the basis of our results, seems to play a key part in neurotransmitter release.

Tetanus toxin is a zinc protein and its inhibition of neurotransmitter release and protease activity depend on zinc.

Abstract: Tetanus and botulinum neurotoxins are the most potent toxins known. They bind to nerve cells, penetrate the cytosol and block neurotransmitter release. Comparison of their predicted amino acid sequences reveals a highly conserved segment that contains the HexxH zinc binding motif of metalloendopeptidases. The metal content of tetanus toxin was then measured and it was found that one atom of zinc is bound to the light chain of tetanus toxin. Zinc could be reversibly removed by incubation with heavy metal chelators. Zn2+ is coordinated by two histidines with no involvement in cysteines, suggesting that it plays a catalytic rather than a structural role. Bound Zn2+ was found to be essential for the tetanus toxin inhibition of neurotransmitter release in Aplysia neurons injected with the light chain. The intracellular activity of the toxin was blocked by phosphoramidon, a very specific inhibitor of zinc endopeptidases. Purified preparations of light chain showed a highly specific proteolytic activity against synaptobrevin, an integral membrane protein of small synaptic vesicles. The present findings indicate that tetanus toxin, and possibly also the botulinum neurotoxins, are metalloproteases and that they block neurotransmitter release via this protease activity.

Short-Term Synaptic Plasticity

Abstract: ▪ Abstract Synaptic transmission is a dynamic process. Postsynaptic responses wax and wane as presynaptic activity evolves. This prominent characteristic of chemical synaptic transmission is a crucial determinant of the response properties of synapses and, in turn, of the stimulus properties selected by neural networks and of the patterns of activity generated by those networks. This review focuses on synaptic changes that result from prior activity in the synapse under study, and is restricted to short-term effects that last for at most a few minutes. Forms of synaptic enhancement, such as facilitation, augmentation, and post-tetanic potentiation, are usually attributed to effects of a residual elevation in presynaptic [Ca2+]i, acting on one or more molecular targets that appear to be distinct from the secretory trigger responsible for fast exocytosis and phasic release of transmitter to single action potentials. We discuss the evidence for this hypothesis, and the origins of the different kinetic phases...

SNAP receptors implicated in vesicle targeting and fusion

Abstract: The N-ethylmaleimide-sensitive fusion protein (NSF) and the soluble NSF attachment proteins (SNAPs) appear to be essential components of the intracellular membrane fusion apparatus. An affinity purification procedure based on the natural binding of these proteins to their targets was used to isolate SNAP receptors (SNAREs) from bovine brain. Remarkably, the four principal proteins isolated were all proteins associated with the synapse, with one type located in the synaptic vesicle and another in the plasma membrane, suggesting a simple mechanism for vesicle docking. The existence of numerous SNARE-related proteins, each apparently specific for a single kind of vesicle or target membrane, indicates that NSF and SNAPs may be universal components of a vesicle fusion apparatus common to both constitutive and regulated fusion (including neurotransmitter release), in which the SNAREs may help to ensure vesicle-to-target specificity.

SNAREs--engines for membrane fusion.

Abstract: Since the discovery of SNARE proteins in the late 1980s, SNAREs have been recognized as key components of protein complexes that drive membrane fusion. Despite considerable sequence divergence among SNARE proteins, their mechanism seems to be conserved and is adaptable for fusion reactions as diverse as those involved in cell growth, membrane repair, cytokinesis and synaptic transmission. A fascinating picture of these robust nanomachines is emerging.

Mechanisms of intracellular protein transport

Abstract: Recent advances have uncovered the general protein apparatus used by all eukaryotes for intracellular transport, including secretion and endocytosis, and for triggered exocytosis of hormones and neurotransmitters. Membranes are shaped into vesicles by cytoplasmic coats which then dissociate upon GTP hydrolysis. Both vesicles and their acceptor membranes carry targeting proteins which interact specifically to initiate docking. A general apparatus then assembles at the docking site and fuses the vesicle with its target.

The synaptic vesicle cycle: a cascade of protein–protein interactions

Abstract: The synaptic vesicle cycle at the nerve terminal consists of vesicle exocytosis with neurotransmitter release, endocytosis of empty vesicles, and regeneration of fresh vesicles. Of all cellular transport pathways, the synaptic vesicle cycle is the fastest and the most tightly regulated. A convergence of results now allows formulation of molecular models for key steps of the cycle. These developments may form the basis for a mechanistic understanding of higher neural function.