Nedd4 is the prototypical protein in a family of E3 ubiquitin ligases. Nedd4 family proteins have a catalytic C-terminal HECT domain and N-terminal C2 domain and several WW domains. The C2 domain made up of nearly 130 amino acids, is thought to be the major lipid binding module of Nedd4 proteins. The Nedd4 family proteins play important roles in cellular activities, for example, hNedd4-2 is involved in the regulation of human ENaC(epithelial sodium channel) activity. My work focuses on two human proteins: Nedd4-1 and Nedd4-2. I have expressed C2 domains of these two proteins and tested their binding properties to different membrane lipids by lipid sedimentation assay and surface plasmon resonance. The C2 domains displayed binding to the anionic plasma membrane containing lipid phosphatidylserine. This indicates they may control plasma membrane specific targeting of Nedd4-1 and -2 in the cell. We are currently investigating their cellular targeting mechanism through expression in different cell lines. We will investigate their membrane targeting mechanism in response to Ca2+ spikes and their interaction with substrates. It is also of keen interest to determine how the lipid membrane plays a role in their activation and substrate recognition.