Association of membrane-associated guanylate kinase-interacting protein-1 with Raf-1

Membrane-associated guanylate kinase-interacting protein (MAGUIN)-1 was ide ntified as a protein interacting with synaptic scaffolding molecule (S-SCAM ) and postsynaptic density (PSD)-95/synapse-associated protein (SAP)SO. MAG UIN-1 has a chimerical molecular structure composed of one sterile alpha mo th, one PSD-95/Dlg-A/ZO-1 (PDZ), and one pleckstrin homology (PH) domain, a nd interacts with the PDZ domains of S SCAM and PSD-95/SAP90 via its carbox yl-terminal PDZ-binding motif. MAGUIN-1 is considered as a mammalian homolo gue of Drosophila CNK which is a Raf-interacting protein implicated in the regulation of eye development. Here we have tested whether MAGUIN-1 interac ts directly with Raf-l. MAGUIN-1 and Raf-l were coimmunoprecipitated hem ra t brain. MAGUIN-1 binds to the kinase domain of Raf-l, and Raf-l binds to t he mid die region of MAGUIN-1 containing the PH domain. However, in contras t to the dominant active mutant of Ki-Ras, which interacts with Raf-l, recr uits it to the plasma membrane from the cytosol, and activates it, MAGUIN-1 neither activates Raf-l nor recruits it to the plasma membrane. MAGUIN-1 m ay link Raf-l to components of synapses assembled by PSD-95/SAP90 and S-SCA M. (C) 2000 Academic Press.