Abstract
Multiprotein complexes mediate static and dynamic functions to establish and maintain cell polarity in both epithelial cells and neurons. Membrane-associated guanylate kinase (MAGUK) proteins are thought to be scaffolding molecules in these processes and bind multiple proteins via their obligate postsynaptic density (PSD)-95/Disc Large/Zona Occludens-1, Src homology 3, and guanylate kinase-like domains. Subsets of MAGUK proteins have additional protein-protein interaction domains. An additional domain we identified in SAP97 called the MAGUK recruitment (MRE) domain binds the LIN-2,7 amino-terminal (L27N) domain of mLIN-2/CASK, a MAGUK known to bind mLIN-7. Here we show that SAP97 binds two other mLIN-7 binding MAGUK proteins. One of these MAGUK proteins, DLG3, coimmunoprecipitates with SAP97 in lysates from rat brain and transfected Madin-Darby canine kidney cells. This interaction requires the MRE domain of SAP97 and surprisingly, both the L27N and L27 carboxyl-terminal (L27C) domains of DLG3. We also demonstrate that SAP97 can interact with the MAGUK protein, DLG2, but not the highly related protein, PALS2. The ability of SAP97 to interact with multiple MAGUK proteins is likely to be important for the targeting of specific protein complexes in polarized cells.
Highlights
Polarized cells such as neurons and epithelia establish and maintain a nonhomogenous plasma membrane distribution of both integral and peripheral membrane proteins [1,2,3]
An additional domain we identified in SAP97 called the Membrane-associated guanylate kinase (MAGUK) recruitment (MRE) domain binds the LIN-2,7 amino-terminal (L27N) domain of mLIN-2/CASK, a MAGUK known to bind mLIN-7
Multiple mLIN-7 Binding Proteins Associate with SAP97— Previous studies have demonstrated that several MAGUK proteins can bind mLIN-7, including mLIN-2/CASK [6, 8, 11] and that mLIN-2/CASK (Fig. 1A) can directly interact with SAP97 [13, 23]
Summary
Polarized cells such as neurons and epithelia establish and maintain a nonhomogenous plasma membrane distribution of both integral and peripheral membrane proteins [1,2,3]. SAP97, a mammalian homolog of the Drosophila tumor suppressor Dlg [19], is a MAGUK protein that was reported to bind mLIN-2/CASK via a newly described MAGUK recruitment (MRE) domain [13, 15]. We show that SAP97 binds two other mLIN-7 associated MAGUKs via this MRE domain. Rat brain lysates were immunoprecipitated with antibodies directed against known mLIN-7 binding proteins including DLG3 and PALS2.
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