Syntaxin Isoforms

Synaptic exocytosis involves three SNARE proteins the R-SNARE synaptobrevin/VAMP (isoforms 1 and 2) on the vesicle, and the Q-SNAREs syntaxin (isoforms 1 and 2) and SNAP-25 on the plasma membrane (Figure 4). Since SNAP-25 has two SNARE-motifs, synaptobrevin, syntaxin, and SNAP-25 together have four SNARE-motifs. Synaptobrevins and SNAP-25 are relatively simple SNARE proteins that are composed of little else besides SNARE motifs and membrane-attachment sequences (a transmembrane region for synaptobrevin, and a cysteine-rich palmitoylated sequence for SNAP-25). Syntaxins, in contrast, are complex proteins. The N-terminal two-thirds of syntaxins include a separate, autonomously folded domain (the so-called Habc-domain), while the C-terminal third is composed of a SNARE motif and transmembrane region just like synaptobrevin. 

A second mechanism that impinges on the localization of transporters is through the association with proteins, the most prominent example being syntaxin. Syntaxin is a t-SNARE protein necessary for the fusion of vesicles with the plasma membrane (see the chapter on exocytosis). On the cell surface syntaxin consistently stabilizes the localization of GABA, noradrenaline, glycine, and 5HT transporters the PKCa isoform can sever the interaction with syntaxin suggesting a general mechanism for transporter internalization. 

Synaptotagmins Membrane proteins with at least 15 isoforms that contain C2 domains bind Ca2+ and phospholipids and interact with neurexins, AP2 and syntaxins. Synaptotagmins 1 and 2 may function as Ca2+ sensors in fast Ca2+-dependent neurotransmitter release... 

Neurexins a protein kinase. A component of active zones that interact with RIM, syntaxin and other proteins. Cell surface proteins with more than 1,000 isoforms generated by alternative splicing from three genes. Neurexins include one of the receptors for aratrotoxin and may function in cell-cell recognition between neurons. 

Syntabulin, isoform 1 Q9NX95 (h) 1) Syntaxin-1 binding protein 2) Golgi-localized syntaphilin-related protein (Golsyn) FU20366 (h) GOLSYN (h) 8q23.2 (h) 663 (h)... 

The vesicle-associated membrane proteins (VAMP or synaptobrevin) occur in three isoforms and are proteins that are anchored to the cytoplasmic portion of synaptic membrane vesicles and secretory granules. VAMP2 and 3 are present in pancreatic beta cells, but the roles of this family of proteins have not been widely studied as markers of NE tumors. In contrast to synaptophysin and other synaptic vesicle proteins, SNAP-25 (synaptosomal protein of 25 KD) and syntaxin are present in the plasma membranes. At present, there are few studies on the application of these markers in diagnostic pathology... 

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