Fig. 8.

Proposed model for the SadA-cortexillin I interaction. Based on our current data, we propose the following model for the SadA tail-cortexillin I (CtxA) interaction. Under adherent conditions, an interaction occurs between the carboxy-terminal tail of SadA via the S924/5 and S940/1 sites and presumably the coiled-coil region of CtxA. This results in a linkage between SadA and the subcortical actin cytoskeleton. Under nonadherent conditions, or during cellular motility, perhaps, an unknown kinase(s) would phosphorylate sites in the SadA tail, resulting in release of CtxA from the SadA tail. This would temporarily disrupt the link between SadA and the actin cytoskeleton. During the processes of cell motility and phagocytosis, the cell must have a dynamic linkage between the actin cytoskeleton and membrane receptor in order to generate the forces necessary for the cell to move or to engulf a particle, respectively. The interaction between SadA and CtxA in our proposed model might be one mechanism that Dictyostelium has developed to perform these tasks.