| Syntaxin proteins, prototypical t-SNAREs of the SNARE superfamily, anchor to target membranes via C-terminal transmembrane domains and mediate docking and fusion specificity across eukaryotic vesicular transport pathways from the ER to the plasma membrane. Characteristic structural elements include a membrane-proximal SNARE motif forming coiled-coil helices for parallel four-helix bundle assembly and an N-terminal Habc domain composed of three α-helices that folds back onto the SNARE motif to enforce a closed, autoinhibited conformation. In this closed state, Munc18 binds tightly to stabilize inactivity and prevent premature SNARE interactions; upon priming by Munc13 or synaptotagmin-Ca2+ signals, the Habc domain unfolds to the open state. This transition enables the syntaxin SNARE motif to zipper with SNAP-25 and the v-SNARE VAMP2 into trans-SNARE complexes that bridge vesicle and plasma membranes, culminating in hemifusion and full fusion driven by NSF/α-SNAP disassembly. Syntaxin-1 isoforms predominate in neuronal presynaptic terminals for fast neurotransmitter release, while syntaxin-4 drives GLUT4 translocation and syntaxin-5 facilitates ER-Golgi anterograde traffic. Direct interactions with voltage-gated ion channels localize fusion sites, while Rab effectors and synaptotagmin sense calcium to accelerate the zippering process. Mutations or proteolytic cleavage by botulinum neurotoxin C truncate syntaxin-1, blocking SNARE assembly and inducing plasma membrane recycling defects, which contributes to neuronal degeneration and synaptic loss in conditions such as botulism and Alzheimer’s disease. |
