SAP-1 (Synapse associated protein- I, SYAP1) is a proline-rich synapse-associated protein originally isolated from synaptic junctional protein preparations of rat brain. It is an essential component of the postsynaptic density (PSD) and is specifically targeted to e, Xenopus/Amphibian,citatory asymmetric type 1 synapses. Functionally, SAP-1 is a postsynaptic key element since it links and attaches the postsynaptic signaling apparatus, e.g. NMDA-receptors, via direct and indirect protein interactions to the actin-based cytoskeleton.