BET1-like protein (also known as Golgi SNARE with a size of 15kDa, GS15 or GOS-15) is a protein required for movement of vesicles with the Golgi. In one hypothesis of how proteins move through the Golgi, vesicles containing proteins are budded from one cisterna and then fuse with the next cisterna in the stack. The fusion of the vesicle to the cisterna membrane requires N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). SNAREs on a transport vesicle are known as v-SNAREs, and those on the target compartment are known as t-SNAREs; the v-SNARE and a t-SNARE form a trans-SNARE complex. GS15 is a v-SNARE protein found in the medial-cisternae of the Golgi apparatus and it forms a complex with three t-SNAREs (Syntaxin5, GS28, and Ykt6) to form a distinct GS15/Syn5/GS28/Ykt6 SNARE complex. This complex is required for endoplasmic reticulum to Golgi transport and intra-Golgi transport [, ].
YKT6 forms complexes with syntaxin-5 (Qa), GS28 (Qb) and either Bet1 (Qc) or GS15 (Qc). This complex regulates the early secretory pathway of eukaryotic cells at the level of the transport from the ER-Golgi intermediate compartment (ERGIC) to the cis-Golgi and transport from the trans-Golgi network to the cis-Golgi, respectively [, ]. YKT6 is a member of the R-SNARE subfamily of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins which contain coiled-coil helices (called SNARE motifs) that mediate the interactions between SNARE proteins, and a transmembrane domain.The SNARE complex mediates membrane fusion, important for trafficking of newly synthesized proteins, recycling of pre-existing proteins and organelle formation. SNARE proteins are classified into four groups, Qa-, Qb-, Qc- and R-SNAREs, depending on whether the residue in the hydrophilic centre layer of the four-helical bundle is a glutamine (Q) or arginine (R). Qa-, as well as Qb- and Qc-SNAREs, are localized to target organelle membranes, while R-SNARE is localized to vesicle membranes. They form unique complexes consisting of one member of each subgroup, that mediate fusion between a specific type of vesicles and their target organelle. Their SNARE motifs form twisted and parallel heterotetrameric helix bundles [].
