Densin-180, a synaptic protein, links to PSD-95 through its direct interaction with MAGUIN-1.
BACKGROUND
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.


CONCLUSIONS
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.
Ohtakara
Kazuhiro
K
Division of Biochemistry, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya, Aichi 464-8681, Japan.
Nishizawa
Miwako
M
Izawa
Ichiro
I
Hata
Yutaka
Y
Matsushima
Satoshi
S
Taki
Waro
W
Inada
Hiroyasu
H
Takai
Yoshimi
Y
Inagaki
Masaki
M
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D000076122:Disks Large Homolog 4 Protein; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D020539:Sequence Analysis, Protein; D012795:Sialoglycoproteins / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C118898:Cnksr2 protein, rat; D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; C504461:LRRC7 protein, human; C504463:Lrrc7 protein, rat; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012795:Sialoglycoproteins; C033652:postsynaptic density proteins