6jx5
Hect domain of AREL1
Structural highlights
FunctionAREL1_HUMAN E3 ubiquitin-protein ligase which accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrates. Inhibits apoptosis by ubiquitinating and targeting for degradation a number of proapoptotic proteins including DIABLO/SMAC, HTRA2 and SEPT4/ARTS which are released from the mitochondrion into the cytosol following apoptotic stimulation.[1] Publication Abstract from PubMedThe HECT E3 ligase family comprises three subfamilies: NEDD4 E3 ubiquitin protein ligase (NEDD4), HECT and RLD domain-containing E3 ubiquitin protein ligase (HERC), and "other." Most previous studies have focused on the NEDD4 subfamily. Apoptosis-resistant E3 ligase 1 (AREL1) belongs to "other" subfamily HECT that inhibits apoptosis by ubiquitinating and degrading proapoptotic proteins. Here, we report the crystal structure of the extended HECT domain of AREL1 (436-823 aa) at 2.4 A resolution and its ubiquitination of the proapoptotic protein second mitochondria-derived activator of caspase (SMAC). We found that the extended HECT domain adopts an inverted, T-shaped, bilobed conformation and harbors an additional loop (567-573 aa) absent in all other HECT members. We also show that the N-terminal extended region (436-482 aa) preceding the HECT domain is indispensable for its stability and activity and that without this region, the HECT domain becomes inactive. AREL1 ubiquitinated SMAC, primarily on Lys-62 and Lys-191. We solved the crystal structure of tetrameric form of SMAC to 2.8 A resolution, revealing the Lys-62 and Lys-191 locations. The AREL1 HECT domain assembled Lys-33-, Lys-48- and Lys-63-linked polyubiquitin chains. Moreover, E701A substitution in the AREL1 HECT domain substantially increased its autopolyubiquitination and SMAC ubiquitination activity, whereas deletion of the last three amino acids at the C terminus completely abrogated AREL1 autoubiquitination and reduced SMAC ubiquitination. Finally, an AREL1-specific ubiquitin variant inhibited SMAC ubiquitination in vitro. Our findings may assist in the development of AREL1 inhibitors that block its anti-apoptotic activity in cancer. Structural insights into a HECT-type E3 ligase AREL1 and its ubiquitination activities in vitro.,Singh S, Ng J, Nayak D, Sivaraman J J Biol Chem. 2019 Nov 15. pii: RA119.010327. doi: 10.1074/jbc.RA119.010327. PMID:31732561[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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