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Ethylmaleimide: A sulfhydryl reagent that is widely used in experimental biochemical studies.SNARE Proteins: A superfamily of small proteins which are involved in the MEMBRANE FUSION events, intracellular protein trafficking and secretory processes. They share a homologous SNARE motif. The SNARE proteins are divided into subfamilies: QA-SNARES; QB-SNARES; QC-SNARES; and R-SNARES. The formation of a SNARE complex (composed of one each of the four different types SNARE domains (Qa, Qb, Qc, and R)) mediates MEMBRANE FUSION. Following membrane fusion SNARE complexes are dissociated by the NSFs (N-ETHYLMALEIMIDE-SENSITIVE FACTORS), in conjunction with SOLUBLE NSF ATTACHMENT PROTEIN, i.e., SNAPs (no relation to SNAP 25.)N-Ethylmaleimide-Sensitive Proteins: ATPases that are members of the AAA protein superfamily (ATPase family Associated with various cellular Activities). The NSFs functions, acting in conjunction with SOLUBLE NSF ATTACHMENT PROTEINS (i.e. SNAPs, which have no relation to SNAP 25), are to dissociate SNARE complexes.Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins: SNARE binding proteins that facilitate the ATP hydrolysis-driven dissociation of the SNARE complex. They are required for the binding of N-ETHYLMALEIMIDE-SENSITIVE PROTEIN (NSF) to the SNARE complex which also stimulates the ATPASE activity of NSF. They are unrelated structurally to SNAP-25 PROTEIN.Vesicular Transport Proteins: A broad category of proteins involved in the formation, transport and dissolution of TRANSPORT VESICLES. They play a role in the intracellular transport of molecules contained within membrane vesicles. Vesicular transport proteins are distinguished from MEMBRANE TRANSPORT PROTEINS, which move molecules across membranes, by the mode in which the molecules are transported.Qa-SNARE Proteins: A subfamily of Q-SNARE PROTEINS which occupy the same position as syntaxin 1A in the SNARE complex and which also are most similar to syntaxin 1A in their AMINO ACID SEQUENCE. This subfamily is also known as the syntaxins, although a few so called syntaxins are Qc-SNARES.R-SNARE Proteins: SNARE proteins where the central amino acid residue of the SNARE motif is an ARGININE. They are classified separately from the Q-SNARE PROTEINS where the central amino acid residue of the SNARE motif is a GLUTAMINE. This subfamily contains the vesicle associated membrane proteins (VAMPs) based on similarity to the prototype for the R-SNAREs, VAMP2 (synaptobrevin 2).Vesicle-Associated Membrane Protein 2: A synaptic membrane protein involved in MEMBRANE FUSION of SYNAPTIC VESICLES with the presynaptic membranes. It is the prototype member of the R-SNARE PROTEINS.Exocytosis: Cellular release of material within membrane-limited vesicles by fusion of the vesicles with the CELL MEMBRANE.Syntaxin 1: A neuronal cell membrane protein that combines with SNAP-25 and SYNAPTOBREVIN 2 to form a SNARE complex that leads to EXOCYTOSIS.Synaptosomal-Associated Protein 25: A ubiquitous target SNARE protein that interacts with SYNTAXIN and SYNAPTOBREVIN. It is a core component of the machinery for intracellular MEMBRANE FUSION. The sequence contains 2 SNARE domains, one is the prototype for the Qb-SNARES, and the other is the prototype for the Qc-SNARES.Membrane Fusion: The adherence and merging of cell membranes, intracellular membranes, or artificial membranes to each other or to viruses, parasites, or interstitial particles through a variety of chemical and physical processes.Qb-SNARE Proteins: A subfamily of Q-SNARE PROTEINS which occupy the same position in the SNARE complex as the N-terminal SNARE domain of SNAP-25 and which also are most similar to the N-terminal region of SNAP-25 in their AMINO ACID SEQUENCE.Qc-SNARE Proteins: A subfamily of Q-SNARE PROTEINS which occupy the same position in the SNARE complex as the C-terminal SNARE domain of SNAP-25 and which also are most similar to the C-terminal region of SNAP-25 in their AMINO ACID SEQUENCE.Munc18 Proteins: A family of proteins involved in intracellular membrane trafficking. They interact with SYNTAXINS and play important roles in vesicular docking and fusion during EXOCYTOSIS. Their name derives from the fact that they are related to Unc-18 protein, C elegans.Membrane Proteins: Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors.Vesicle-Associated Membrane Protein 3: A member of the vesicle associated membrane protein family. It has a broad tissue distribution and is involved in MEMBRANE FUSION events of the endocytic pathways.Syntaxin 16: A ubiquitously expressed member of the syntaxin subfamily of SNARE proteins that localizes to the GOLGI APPARATUS.Secretory Vesicles: Vesicles derived from the GOLGI APPARATUS containing material to be released at the cell surface.Synaptotagmin I: A vesicular transport protein expressed predominately in NEURONS. Synaptotagmin helps regulate EXOCYTOSIS of SYNAPTIC VESICLES and appears to serve as a calcium sensor to trigger NEUROTRANSMITTER release. It also acts as a nerve cell receptor for certain BOTULINUM TOXINS.Tetanus Toxin: Protein synthesized by CLOSTRIDIUM TETANI as a single chain of ~150 kDa with 35% sequence identity to BOTULINUM TOXIN that is cleaved to a light and a heavy chain that are linked by a single disulfide bond. Tetanolysin is the hemolytic and tetanospasmin is the neurotoxic principle. The toxin causes disruption of the inhibitory mechanisms of the CNS, thus permitting uncontrolled nervous activity, leading to fatal CONVULSIONS.Synaptic Vesicles: Membrane-bound compartments which contain transmitter molecules. Synaptic vesicles are concentrated at presynaptic terminals. They actively sequester transmitter molecules from the cytoplasm. In at least some synapses, transmitter release occurs by fusion of these vesicles with the presynaptic membrane, followed by exocytosis of their contents.Golgi Apparatus: A stack of flattened vesicles that functions in posttranslational processing and sorting of proteins, receiving them from the rough ENDOPLASMIC RETICULUM and directing them to secretory vesicles, LYSOSOMES, or the CELL MEMBRANE. The movement of proteins takes place by transfer vesicles that bud off from the rough endoplasmic reticulum or Golgi apparatus and fuse with the Golgi, lysosomes or cell membrane. (From Glick, Glossary of Biochemistry and Molecular Biology, 1990)Synaptotagmins: A family of vesicular transport proteins characterized by an N-terminal transmembrane region and two C-terminal calcium-binding domains.Nerve Tissue ProteinsProtein Transport: The process of moving proteins from one cellular compartment (including extracellular) to another by various sorting and transport mechanisms such as gated transport, protein translocation, and vesicular transport.Botulinum Toxins: Toxic proteins produced from the species CLOSTRIDIUM BOTULINUM. The toxins are synthesized as a single peptide chain which is processed into a mature protein consisting of a heavy chain and light chain joined via a disulfide bond. The botulinum toxin light chain is a zinc-dependent protease which is released from the heavy chain upon ENDOCYTOSIS into PRESYNAPTIC NERVE ENDINGS. Once inside the cell the botulinum toxin light chain cleaves specific SNARE proteins which are essential for secretion of ACETYLCHOLINE by SYNAPTIC VESICLES. This inhibition of acetylcholine release results in muscular PARALYSIS.Cytoplasmic Vesicles: Membrane-limited structures derived from the plasma membrane or various intracellular membranes which function in storage, transport or metabolism.Cell Membrane: The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.PC12 Cells: A CELL LINE derived from a PHEOCHROMOCYTOMA of the rat ADRENAL MEDULLA. PC12 cells stop dividing and undergo terminal differentiation when treated with NERVE GROWTH FACTOR, making the line a useful model system for NERVE CELL differentiation.Protein Binding: The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.