Rs. Walikonis et al., Densin-180 forms a ternary complex with the alpha-subunit of Ca2+/calmodulin-dependent protein kinase II and alpha-actinin, J NEUROSC, 21(2), 2001, pp. 423-433
Densin-180 is a transmembrane protein that is tightly associated with the p
ostsynaptic density in CNS neurons and is postulated to function as a synap
tic adhesion molecule. Here we report the identification of the alpha -subu
nit of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and alpha -acti
nin-4 as potential binding partners for the densin-180 intracellular segmen
t. We demonstrate by yeast two-hybrid and biochemical assays that the intra
cellular portion of densin-180, the alpha -subunit of CaMKII (CaMKII alpha)
, and alpha -actinin interact with each other at distinct binding sites and
can form a ternary complex stabilized by multiple interactions. Densin-180
binds specifically to the association domain of CaMKII alpha and does not
bind with high affinity to holoenzymes of CaMKII that contain beta -subunit
. The PDZ (PSD-95, DIg, Z0-1) domain of densin contributes to its binding t
o alpha -actinin. A distinct domain of alpha -actinin interacts with the ki
nase domains of both alpha and beta -subunits of CaMKII. Autophosphorylatio
n of CaMKII increases its affinity for densin-180 from an EC50 of <1 mm to
an EC50 of <75-150 nM. In contrast, phosphorylation of densin-180 by CaMKII
at serine-1397 only slightly decreases its affinity for CaMKII. The specif
ic interaction of densin-180 with holoenzymes of CaMKII containing only alp
ha -subunit and the increased affinity of CaMKII for densin-180 after autop
hosphorylation suggest that densin-180 may be involved in localization of a
ctivated CaMKII synthesized in dendrites.