Spartin associates with lipid droplets and possesses a PY motif that recruits the ubiquitin ligase AIP4 (or other Nedd4-family ubiquitin ligases) via the AIP4 WW domains. Via its catalytic HECT domain, AIP4 promotes the ubiquitination of lipid-droplet-associated proteins, such as adipophilin, leading to regulation of turnover of the lipid droplets. Thus, spartin functions as an adaptor protein to promote ubiquitination (Ub) of lipid-droplet-associated proteins. In the absence of spartin, the catalytic activity of AIP4 is inhibited by intramolecular interactions (not shown).
Alberts and Rotin BMC Biology 2010 8:94 doi:10.1186/1741-7007-8-94