TRAPPC4 is a postsynaptic protein belonging to the TRAPPC4 subfamily of the TRAPP small subunits family of proteins. Expressed in neurons and localizing to the Golgi apparatus, TRAPPC4 is believed to be involved in vesicular transport from the endoplasmic reticulum (ER) to the Golgi, functioning as a component of the multisubunit transport protein particle (TRAPP) complex. Similar to other proteins involved in vesicular transport or synaptic function, TRAPPC4 contains a nonclassical PDZ domain, a TRAPPC1-like domain and a C-terminus that is similar to a short segment of RyR. Via its nonclassical PDZ domain, TRAPPC4 binds to the C-terminal EFYA motif of Syndecan-2, suggesting that TRAPPC4 may play an important role in dendritic spine morphogenesis through membrane-trafficking.