Prosapip1 is a binding partner of the postsynaptic density (PSD) protein ProSAP2/Shank3, a major scaffolding protein in excitatory brain synapses.  Prosapip1 is thought to bind ProSAP2/Shank3 through ProSAP2/Shank3’s PDZ domain and link it in turn to the Spine-associated Rap-Gap (SPAR). Prosapip1 shares significant homology with another PSD protein, PSD-Zip70, with both coding for a Fez1 domain that can be found in a total of four related protein, forming a novel family of scaffolding molecules termed ‘Fezzins’. Recent studies show that Prosapip1 can be found in endocrine cells in which it is localized primarily in the hormone-storing compartment of these cells, suggesting that Prosapip1 may have other functions in non-neuronal cells.