SEC22 forms complexes with syntaxin 18 (Qa), Sec20 (Qb) and USE1 (Qc), and with syntaxin 5 (Qa), GS27 (Qb) and Bet1 (Qc). These complexes are involved in the transport from cis-Golgi to the endoplasmic reticulum (ER) and in the transport from endoplasmic reticulum (ER) to the ER-Golgi intermediate compartment (ERGIC), respectively. SEC22 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 center 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",