PSD 93 is believed to participate in the clustering of certain proteins, including N-methyl-D-aspartate (NMDA) receptors and shaker-type potassium channels at the synaptic membrane. There are two principal modes of interaction between PSD 93 and other proteins. NMDA receptors and shaker-type potassium channels both share C-terminal sequence homology consisting of a threonine/serine-X-valine-COOH (T/SXV) motif. Other neuronal proteins that share this motif (beta 1 adrenergic receptor, some serotonin receptors, some sodium channel subunits, and additional potassium channel subunits) may interact with PSD 93 by binding to its PDZ domains. Neuronal nitric oxide synthase (nNOS), which lacks the T/SXV motif but which has its own PDZ domain, has been shown to associate with PSD 93 in vitro through a pseudo-homotypic PDZ-PDZ interaction.