Syntaxins are a family of

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

integrated Q-SNARE

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...

participating in

exocytosis Exocytosis is a term for the active transport process that transports large molecules from cell to the extracellular area. Hormones, proteins and neurotransmitters are examples of large molecules that can be transported out of the cell. Exocytosis ...

Domains

Syntaxins possess a single C-terminal transmembrane domain, a SNARE domain (known as H3), and an N-terminal regulatory domain (Habc). Syntaxin 17 may have two transmembrane domains. * The SNARE (H3) domain binds to both synaptobrevin and SNAP-25 forming the core SNARE complex. Formation of this stable SNARE core complex is believed to generate the free energy required to initiate fusion between the vesicle membrane and plasma membrane. * The N-terminal Habc domain is formed by 3 α-helices and when collapsed onto its own H3 helix forms an inactive "closed" syntaxin conformation. This closed conformation of syntaxin is believed to be stabilized by binding of Munc-18 (nSec1), although more recent data suggests that nSec1 may bind to other conformations of syntaxin, as well. The "open" syntaxin conformation is the conformation that is competent to form into SNARE core complexes.

Function

''In vitro'' syntaxin per se is sufficient to drive spontaneous calcium independent fusion of synaptic vesicles containing v-SNAREs. More recent and somewhat controversial amperometric data suggest that the transmembrane domain of Syntaxin1A may form part of the fusion pore of exocytosis.

Binding

Syntaxins bind

synaptotagmin Synaptotagmins (SYTs) constitute a family of cell membrane, membrane-trafficking proteins that are characterized by an N-terminal transmembrane region (TMR), a variable linker, and two C-terminal C2 domains - C2A and C2B. There are 17 Protein isof ...

in a calcium-dependent fashion and interact with voltage dependent calcium and potassium channels via the C-terminal H3 domain. Direct syntaxin-channel interaction is a suitable molecular mechanism for proximity between the fusion machinery and the gates of Ca²⁺ entry during depolarization of the presynaptic axonal boutons. The Sec1/Munc18 protein family is known to bind to Syntaxin and regulate Syntaxins machinery. Munc18-1 binds to Syntaxin 1A via two distinct sites referred as

N-terminus The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amin ...

binding and "closed" conformation that incorporates both the central Habc domain and the SNARE core domain. Munc18-1 binding to the N-terminus of Syntaxin-1 is thought to facilitate Syntaxin-1 interaction with another SNARE, while binding to the "closed" conformation of Syntaxin-1 is believed to be inhibitory. Recently published data show that alternative spliced Syntaxin 1 (STX1B) which lacks the transmembrane domain localizes in the nuclei.

Genes

Human genes encoding syntaxin proteins include: * STX1A, STX1B, STX2, STX3,

STX4 Syntaxin-4 is a protein that in humans is encoded by the ''STX4'' gene. Interactions STX4 has been shown to Protein-protein interaction, interact with: * Gelsolin, * NAPA (gene), NAPA, * RAB4A, * SNAP-25, * SNAP23, * STXBP1, * STXBP5, ...

, STX5, STX6, STX7, STX8, * STX10, STX11, STX12, STX16, STX17, STX18, STX19

References

External links