The pre-vacuolar t-SNARE AtPEP12p forms a 20S complex that dissociates in the presence of ATP

Many proteins are transported to the plant vacuole through the secretory pathway in small transport vesicles by a series of vesicle budding and fusion reactions. Vesicles carrying vacuolar cargo bud from the trans-Golgi network are thought to fuse with a pre-vacuolar compartment before being finally transported to the vacuole. In mammals and yeast, the fusion of a vesicle with its target organelle is mediated by a 20S protein complex containing membrane and soluble proteins that appear to be conserved between different species. A number of membrane proteins have been identified in plants that show sequence similarity with a family of integral membrane proteins (t-SNAREs) on target organelles that are required for the fusion of transport vesicles with that organelle. However, the biochemical function of these proteins has remained elusive. Here, we demonstrate for the first time the formation of a 20S complex in plants that has characteristics of complexes involved in vesicle fusion. This complex contains AtPEP12p, an Arabidopsis protein thought to be involved in protein transport to the prevacuolar compartment. In addition, we have shown that AtPEP12p can bind to alpha-SNAP, indicating that AtPEP12p does indeed function as a SNAP receptor or SNARE. These preliminary data suggest that AtPEP12p may function jointly with alpha-SNAP and NSF in the fusion of transport vesicles containing vacuolar cargo proteins with the pre-vacuolar compartment.