AbstractBackground: Densin‐180, a brain‐specific protein highly concentrated at the postsynaptic density (PSD), belongs to the LAP [leucine‐rich repeats and PSD‐95/Dlg‐A/ZO‐1 (PDZ) domains] family of proteins, some of which play fundamental roles in the establishment of cell polarity.
Results: To identify new Densin‐180‐interacting proteins, we screened a yeast two‐hybrid library using the COOH‐terminal fragment of Densin‐180 containing the PDZ domain as bait, and we isolated MAGUIN‐1 as a Densin‐180‐binding protein. MAGUIN‐1, a mammalian homologue of Drosophila connector enhancer of KSR (CNK), is known to interact with PSD‐95 and has a short isoform, MAGUIN‐2. The Densin‐180 PDZ domain bound to the COOH‐terminal PDZ domain‐binding motif of MAGUIN‐1. Densin‐180 co‐immunoprecipitated with MAGUIN‐1 as well as with PSD‐95 from the rat brain. In dissociated hippocampal neurones Densin‐180 co‐localized with MAGUINs and PSD‐95, mainly at neuritic spines. In transfected cells, Densin‐180 formed a ternary complex with MAGUIN‐1 and PSD‐95, whereas no association was detected between Densin‐180 and PSD‐95 in the absence of MAGUIN‐1. MAGUIN‐1 formed a dimer or multimer via the COOH‐terminal leucine‐rich region which is present in MAGUIN‐1 but not in ‐2. Among the PDZ domains of PSD‐95, the first was sufficient for interaction with MAGUIN‐1.
Conclusion: These results suggest that the potential to dimerize or multimerize allows MAGUIN‐1 to bind simultaneously to both Densin‐180 and PSD‐95, leading to the ternary complex assembly of these proteins at the postsynaptic membrane.
