THE ROD CGMP PHOSPHODIESTERASE DELTA-SUBUNIT DISSOCIATES THE SMALL GTPASE RAB13 FROM MEMBRANES

Small Rab GTPases are involved in the regulation of membrane trafficki ng. They cycle between cytosolic and membrane-bound forms. These membr ane association/dissociation are tightly controlled by regulatory prot eins. To search for proteins interacting with Rab13, a small GTPase as sociated with vesicles in fibroblasts and predominantly with tight jun ctions in epithelial cells, we screened a HeLa two-hybrid cDNA Library and isolated a clone encoding a protein of 17.4 kDa. This protein, al most identical to the bovine rod cGMP phosphodiesterase delta subunit, was named human delta-PDE. The delta-PDE binds specifically to Rab13. It exhibits two putative C-terminal sequences necessary for the inter action with PDZ (PSD95, Dig, ZO-1) domains contained in many proteins localized to specific plasma membrane microdomains. Immunofluorescence microscopic studies revealed that the vesicular stomatitis virus (VSV )tagged F-PDE is localized in vesicular structures accumulated near th e plasma membrane in epithelial cells. Deletion of the PDZ binding mot ifs impair VSV-S-PDE subcellular distribution. Purified recombinant S- PDE had the capacity to dissociate Rab13 from cellular membranes. Our data support the proposal that S-PDE, but not GDP dissociation inhibit or, may serve to control the dynamic of the association of Rab13 with cellular membranes.