Pleckstrin Homology Domain 1 of Mouse R1-Syntrophin Binds Phosphatidylinositol 4,5-Bisphosphate †

ABSTRACT: Mouse R1-syntrophin sequences were produced as chimeric fusion proteins in bacteria and found to bind phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P 2 ). Half-maximal binding occurred at 1.9 µM PtdIns4,5P 2 and when 1.2 PtdIns4,5P 2 were added per syntrophin. Binding was specific for PtdIns4,5P 2 and did not occur with six other tested lipids including the similar phosphatidylinositol 4-phosphate. Binding was localized to the N-terminal pleckstrin homology domain (PH1); the second, C-terminal PH2 domain did not bind lipids. Key residues in PtdIns4,5P 2 binding to a PH domain were found to be conserved in R-syntrophins' PH1 domains and absent in PH2 domains, suggesting a molecular basis for binding