SALMs 1-3 interact with the PDZ domain containing proteins PSD 95 (DLG4) and synapse associated protein 97 (SAP97 or DLG1) and SAP102 (DLG3), based on yeast 2-hybrid assays (Wang et al. 2006, Ko et al. 2006) and coimmunoprecipitations from detergent solubilized brain (Wang et al. 2006, Ko et al. 2006, Mah et al. 2010) and transiently transfected mammalian cells (Morimura et al., 2006, Wang et al. 2006). PDZ proteins play a central role in organizing functionally diverse membrane proteins at the synapse (Wang et al. 2006, Zheng et al. 2011). PSD-95 family members are abundant postsynaptic scaffolding proteins at excitatory synapses. SALM1 (Wang et al. 2006), SALM2 (Ko et al. 2006), SALM3 and SALM5 (Mah et al. 2010) proteins are enriched in synaptic fractions. SALM5 forms a weak complex with PSD-95, an abundant postsynaptic scaffolding protein at excitatory synapse most likely through indirect interactions (Mah et al. 2010). SALM3 and SALM5, but not other SALMs, induce presynaptic differentiation in contacting axons (Mah et al. 2010).