What do proteins need to reach different vacuoles?
Vacuolar proteins begin their life in the endoplasmic reticulum (ER) where they enter the secretory pathway. The information necessary for the correct delivery of soluble proteins to vacuoles has been found in propeptides that might be located at the N-terminus or the C-terminus of the protein, or might be internal. Without these propeptides, vacuolar proteins are secreted. For membrane proteins, both the transmembrane domains and the cytosolic tails are important for sorting to the tonoplast. Available information suggests that soluble proteins destined for the lytic vacuoles are transported through the Golgi complex and then sorted by a receptor that delivers them to a prevacuolar compartment. Proteins destined for the storage vacuoles might or might not travel through the Golgi complex and are packed into large, dense vesicles before being delivered to the storage vacuoles. Sorting of storage proteins occurs along the Golgi complex or in the ER itself and appears to involve self-aggregation.