APC10-like DOC1 domain of HECTD3, a HECT E3 ubiquitin ligase protein that mediates substrate ubiquitination.
This model represents the APC10/DOC1 domain present in HECTD3, a HECT (Homologous to the E6-AP Carboxyl Terminus) E3 ubiquitin ligase protein. HECT E3 ubiquitin ligases mediate substrate ubiquitination (or ubiquitylation), and are a component of the ubiquitin-26S proteasome pathway for selective proteolytic degradation. They also regulate the trafficking of many receptors, channels, transporters and viral proteins. HECTD3 (HECT domain-containing protein3) contains a C-terminal HECT domain with the active site for ubiquitin transfer onto substrates, and an N-terminal APC10/DOC1 domain, which is responsible for substrate recognition and binding. HECTD3 specifically recognizes the Trio-binding protein, Tara (Trio-associated repeat on actin), implicated in regulating actin cytoskeletal, cell motility and cell growth. Tara also binds to TRF1 and may participate in telomere maintenance and/or mitotic regulation through interacting with TRF1. HECTD3 interacts with and promotes the ubiquitination of Syntaxin 8, an endosomal syntaxin proposed to mediate distinct steps of endosomal protein trafficking. HECTD3-mediated Syntaxin 8 degradation has been suggested to contribute to the pathophysiology of neurodegenerative diseases.