Tetanus toxin is an extremely potent neurotoxin produced by the vegetative cell of Clostridium tetani in anaerobic conditions, causing tetanus. It has no known function for clostridia in the soil environment where they are normally encountered. It is also called spasmogenic toxin, or TeNT. The LD50 of this toxin has been measured to be approximately 2.5-3 ng/kg, making it second only to the related botulinum toxin (LD50 2 ng/kg) as the deadliest toxin in the world. However, these tests are conducted solely on mice, which may react to the toxin differently from humans and other animals.
N-ethylmaleimide-sensitive factor, also known as NSF or N-ethylmaleimide sensitive fusion proteins, is an enzyme which in humans is encoded by the NSF gene.
In a neuron, synaptic vesicles store various neurotransmitters that are released at the synapse. The release is regulated by a voltage-dependent calcium channel. Vesicles are essential for propagating nerve impulses between neurons and are constantly recreated by the cell. The area in the axon that holds groups of vesicles is an axon terminal or "terminal bouton". Up to 130 vesicles can be released per bouton over a ten-minute period of stimulation at 0.2 Hz. In the visual cortex of the human brain, synaptic vesicles have an average diameter of 39.5 nanometers (nm) with a standard deviation of 5.1 nm.
SNARE proteins – "SNAPREceptor" – are a large protein family consisting of at least 24 members in yeasts and more than 60 members in mammalian cells. The primary role of SNARE proteins is to mediate vesicle fusion – the fusion of vesicles with the target membrane; this notably mediates exocytosis, but can also mediate the fusion of vesicles with membrane-bound compartments. The best studied SNAREs are those that mediate the neurotransmitter release of synaptic vesicles in neurons. These neuronal SNAREs are the targets of the neurotoxins responsible for botulism and tetanus produced by certain bacteria.
Vesicle associated membrane proteins (VAMP) are a family of SNARE proteins with similar structure, and are mostly involved in vesicle fusion.
Synaptosomal-Associated Protein, 25kDa (SNAP-25) is a t-SNARE protein that is encoded by the SNAP25 gene in humans. SNAP-25 is a component of the trans-SNARE complex, which is proposed to account for the specificity of membrane fusion and to directly execute fusion by forming a tight complex that brings the synaptic vesicle and plasma membranes together.
Complexin (also known as synaphin) refers to a one of a small set of eukaryotic cytoplasmic neuronal proteins which binds to the SNARE protein complex (SNAREpin) with a high affinity. These are called synaphin 1 and 2. In the presence of Ca2+, the transport vesicle protein synaptotagmin displaces complexin, allowing the SNARE protein complex to bind the transport vesicle to the presynaptic membrane.
Syntaxin-1A is a protein that in humans is encoded by the STX1A gene.
Synaptosomal-associated protein 23 is a protein that in humans is encoded by the SNAP23 gene. Two alternative transcript variants encoding different protein isoforms have been described for this gene.
Vesicle-associated membrane protein 2 (VAMP2) is a protein that in humans is encoded by the VAMP2 gene.
Synaptobrevin-like protein 1 (SYBL1), also known as vesicle-associated membrane protein 7 (VAMP7), is a protein that in humans is encoded by the VAMP7, or SYBL1, gene.
Vesicle-associated membrane protein 3 is a protein that in humans is encoded by the VAMP3 gene.
Vesicle-associated membrane protein 8 is a protein that in humans is encoded by the VAMP8 gene.
Vesicle-associated membrane protein 4 is a protein that in humans is encoded by the VAMP4 gene.
Vesicle-associated membrane protein 1 (VAMP1) is a protein that in humans is encoded by the VAMP1 gene.
Vesicle-associated membrane protein 5 also known as VAMP5 is a human gene which encodes a member of the synaptobrevin protein family.
The ribbon synapse is a type of neuronal synapse characterized by the presence of an electron-dense structure, the synaptic ribbon, that holds vesicles close to the active zone. It is characterized by a tight vesicle-calcium channel coupling that promotes rapid neurotransmitter release and sustained signal transmission. Ribbon synapses undergo a cycle of exocytosis and endocytosis in response to graded changes of membrane potential. It has been proposed that most ribbon synapses undergo a special type of exocytosis based on coordinated multivesicular release. This interpretation has recently been questioned at the inner hair cell ribbon synapse, where it has been instead proposed that exocytosis is described by uniquantal release shaped by a flickering vesicle fusion pore.
Vesicle fusion is the merging of a vesicle with other vesicles or a part of a cell membrane. In the latter case, it is the end stage of secretion from secretory vesicles, where their contents are expelled from the cell through exocytosis. Vesicles can also fuse with other target cell compartments, such as a lysosome. Exocytosis occurs when secretory vesicles transiently dock and fuse at the base of cup-shaped structures at the cell plasma membrane called porosome, the universal secretory machinery in cells. Vesicle fusion may depend on SNARE proteins in the presence of increased intracellular calcium (Ca2+) concentration.
Munc-18 proteins are the mammalian homologue of UNC-18 and are a member of the Sec1/Munc18-like (SM) protein family. Munc-18 proteins have been identified as essential components of the synaptic vesicle fusion protein complex and are crucial for the regulated exocytosis of neurons and neuroendocrine cells.
Zero ionic layer is the main site of interaction in the core SNARE complex. Dipole-dipole interactions take place between 3 glutamine (Q) residues and 1 arginine (R) residue exposed in this layer. Despite that, the majority of the SNARE complex is hydrophobic because of the leucine zipper. Extensively studied layers within the SNARE alpha-helical bundle are designated from "-7" to "+8". Zero ionic layer is at the center of the bundle, and thus designated as "0" layer.
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