Densin-180 is a synaptic transmembrane protein that is tightly associated with the postsynaptic density in CNS neurons and is postulated to function as a synaptic adhesion molecule. Densin-180 is a brain-specific momber of the O-sialoglycoprotein family which is highly concentrated at synapses along dendrites. The sequence of densin-180 contains 17 leucine-rich repeats, a sialomucin domain, an apparent transmembrane domain, and a PDZ (PSD-95, DIg, Z0-1) domain. The PDZ domain contributes to its binding to a-actinin. The intracellular portion of densin-180, CaMKIIa, interacts with a-actinin at distinct binding sites and, together, they form a ternary complex stabilized by multiple interactions.