Recombinant Human Syntaxin 4 Protein, CF

Syntaxin 4 (STX4) is a widely expressed type IV transmembrane protein that is a member of the syntaxin family of t‑SNARE (target‑Soluble NSF [N‑ethylmaleimide‑sensitive factor] Attachment REceptor) membrane fusion proteins (1, 2). For membrane fusion, VAMPs (Vesicle‑Associated Membrane Proteins, also called Synaptotagmins) as v‑SNAREs on donor (vesicle) membranes interact with t‑SNAREs and SNAPs (Soluble NSF Attachment Proteins) on target (cell surface) membranes, with SM (Sec1/Munc18-like) accessory proteins acting as catalysts for fusion (2). Human Syntaxin 4 cDNA encodes 297 amino acids (aa) including  basolateral targeting motif for epithelial cells (aa 24‑29), a coiled‑coil domain termed Habc (aa 43‑163), an S‑nitrosylation site which regulates fusion (aa 141), a hinge region, a t‑SNARE domain (aa 200‑262), and a C‑terminal transmembrane domain (aa 276‑296) (1‑4). Within aa 1‑183, human Syntaxin 4 shares 89% aa sequence homology with mouse and rat, and 94‑95% with canine, bovine, equine, porcine, feline and ovine Syntaxin 4. Among its known roles, Syntaxin 4 and SNAP‑23 or SNAP‑25 associate with VAMP‑2 for fusion of GLUT4‑containing vesicles with the plasma membrane in muscle and adipose cells (1, 5). It is required for exocytosis of insulin from pancreatic beta‑cells (3, 6, 7). With SNAP23 and VAMP‑3, it allows endosome recycling to extend podosomes during macrophage migration (7‑9). It establishes polarization of epithelial cells, specifying basolateral sorting of proteins (4, 10). It mediates postsynaptic activity‑dependent exocytosis in neural cell dendritic spines (11). It is involved in exocytosis of ANP from cardiomyocytes (12). In FAS‑mediated apoptosis, it allows translocation of acid sphingomyelinase to the cell surface (13). Syntaxin 4 binds F‑actin and gelsolin, linking the plasma membrane with, or releasing it from, the actin cytoskeleton (6, 7).