Structure and function of sorting nexin 9 (SNX9)

Project description

Sorting nexins are proteins that participate in different sorting events in the eukaryotic cell. Sorting nexin 9 (SNX9) was discovered by us as a protein in cytosol that interacted with clathrin, adaptor protein 2 (AP-2), and dynamin-2 (Dyn2), all proteins with crucial roles in the endocytic machinery. We revealed that SNX9 is enrolled in clathrin-mediated endocytosis since SNX9 co-localized with endocytic proteins at the plasma membrane, and overexpression of truncated variants of SNX9 abolished the uptake of transferrin into the cell. SNX9 was found in a resting complex with Dyn2 in the cytosol. Activation of the complex suggested that SNX9 functions as a mediator of Dyn2 recruitment to the membrane.

We plan to continue the investigation of SNX9 to delineate the function of its different domains. In particular, we want to understand how the cytosolic SNX9/Dyn2 complex is activated, how the molecules assemble on the membrane, and how they interact with clathrin and AP-2. We will also look into putative additional functions for SNX9, such as in actin dynamics.

The methodology includes in vitro protein-binding and liposome-binding assays together with studies in cells after depletion of endogenous SNX9 and expression of mutated proteins. The studies focus on the molecular mechanisms of protein and lipid interactions at the plasma membrane. The outcome of this project will aid in the understanding of membrane turnover, receptor down-regulation and cell behavior.