In molecular biology, autophagocytosis associated protein Atg3 is the E2 enzyme for the LC3 lipidation process. It is essential for autophagocytosis. The super protein complex, the Atg16L complex, consists of multiple Atg12-Atg5 conjugates. Atg16L has an E3-like role in the LC3 lipidation reaction. The activated intermediate, LC3-Atg3 (E2), is recruited to the site where the lipidation takes place.
Atg3 catalyses the conjugation of Atg8 and phosphatidylethanolamine (PE). Atg3 has an alpha/beta-fold, and its core region is topologically similar to canonical E2 enzymes. Atg3 has two regions inserted in the core region and another with a long alpha-helicalstructure that protrudes from the core region as far as 30 A. It interacts with atg8 through an intermediate thioesterbond between Cys-288 and the C-terminal Gly of atg8. It also interacts with the C-terminal region of the E1-like atg7 enzyme.
Autophagocytosis is a starvation-induced process responsible for transport of cytoplasmic proteins to the lysosome/vacuole. Atg3 is a ubiquitin like modifier that is topologically similar to the canonical E2 enzyme. It catalyses the conjugation of Atg8 and phosphatidylethanolamine.
Atg3 consists of three domains, an N-terminal domain, a catalytic domain and a C-terminal domain. The catalytic domain contains a cysteine residue within an HPC motif, this is the putative active-site residue for recognition of the Apg5 subunit of the autophagosome complex. The small C-terminal domain is likely to be a distinct binding region for the stability of the autophagosome complex. It carries a highly characteristic conserved FLKF sequence motif.
^Yamada Y, Suzuki NN, Hanada T, Ichimura Y, Kumeta H, Fujioka Y, Ohsumi Y, Inagaki F (March 2007). "The crystal structure of Atg3, an autophagy-related ubiquitin carrier protein (E2) enzyme that mediates Atg8 lipidation". J. Biol. Chem.282 (11): 8036–43. doi:10.1074/jbc.M611473200. PMID17227760.
^Tanida I, Tanida-Miyake E, Komatsu M, Ueno T, Kominami E (April 2002). "Human Apg3p/Aut1p homologue is an authentic E2 enzyme for multiple substrates, GATE-16, GABARAP, and MAP-LC3, and facilitates the conjugation of hApg12p to hApg5p". J. Biol. Chem.277 (16): 13739–44. doi:10.1074/jbc.M200385200. PMID11825910.
^Mizushima N, Yoshimori T, Ohsumi Y (December 2002). "Mouse Apg10 as an Apg12-conjugating enzyme: analysis by the conjugation-mediated yeast two-hybrid method". FEBS Lett.532 (3): 450–4. doi:10.1016/S0014-5793(02)03739-0. PMID12482611.