Ca2+-calmodulin interacts with DdCAD-1 and promotes DdCAD-1 transport by contractile vacuoles in Dictyostelium cells

Abstract

The Ca2+-dependent cell-cell adhesion molecule DdCAD-1, encoded by the cadA gene of Dictyostelium discoideum, is synthesized at the onset of development as a soluble protein and then transported to the plasma membrane by contractile vacuoles. Calmodulin associates with contractile vacuoles in a Ca2+-dependent manner, and co-localizes with DdCAD-1 on the surface of contractile vacuoles. Bioinformatics analysis revealed multiple calmodulin-binding motifs in DdCAD-1. Co-immunoprecipitation and pull-down studies showed that only Ca2+-bound calmodulin was able to bind DdCAD-1. Structural integrity of DdCAD-1, but not the native conformation, was required for its interaction with calmodulin. To investigate the role of calmodulin in the import of DdCAD-1 into contractile vacuoles, an in vitro import assay consisting of contractile vacuoles derived from cadA- cells and recombinant proteins was employed. Prior stripping of the bound calmodulin from contractile vacuoles by EGTA impaired import of DdCAD-1, which was restored by addition of exogenous calmodulin. The calmodulin antagonists W-7 and compound 48/80 blocked the binding of calmodulin onto stripped contractile vacuoles, and inhibited the import of DdCAD-1. Together, the data show that calmodulin forms a complex with DdCAD-1 and promotes the docking and import of DdCAD-1 into contractile vacuoles. Structured digital abstract CaM physically interacts with DdCAD-1 by pull down (View Interaction: 1, 2) DdCAD-1 binds to CaM by far western blotting (View interaction) DdCAD-1 physically interacts with CaM by anti bait coimmunoprecipitation (View interaction) The Ca 2+-dependent cell-cell adhesion molecule DdCAD-1 in Dictyostelium discoideum is synthesized as soluble protein and transported to the plasma membrane via contractile vacuoles. Calmodulin binds DdCAD-1 in a Ca 2+-dependent manner to form a complex which promotes the docking of DdCAD-1 onto the vacuole membrane. Calmodulin also facilitates the translocation of DdCAD-1 into the vacuole lumen. © 2013 The Authors Journal compilation © 2013 FEBS.