InterPro domain: IPR042526

Macroautophagy is a bulk degradation process induced by starvation in eukaryotic cells. In yeast, 15 Atg proteins coordinate the formation of autophagosomes. The pre-autophagosomal structure contains at least five Atg proteins: Atg1p, Atg2p, Atg5p, Aut7p/Atg8p and Atg16p. It is found in the vacuole [ 1 , 2 ]. The C-terminal glycine of Atg12p is conjugated to a lysine residue of Atg5p via an isopeptide bond. During autophagy, cytoplasmic components are enclosed in autophagosomes and delivered to lysosomes/vacuoles. Autophagy protein 16 (Atg16) has been shown to be bind to Atg5 and is required for the function of the Atg12p-Atg5p conjugate [ 3 ]. Autophagy protein 5 (Atg5) is directly required for the import of aminopeptidase I via the cytoplasm-to-vacuole targeting pathway [ 4 ].

This superfamily represents the helix rich domain (HR) found in Atg5.

Atg5 comprises two ubiquitin-like domains that flank a helix-rich domain. The N- and C-terminal ubiquitin-like domains are called UblA and UblB, respectively, and the helix-rich domain between UblA and UblB, is called HR. Both UblA and UblB comprise a five-stranded -sheet and two-helices, which is a conserved feature in all ubiquitin superfamily proteins. The HR domain consists of three alpha helices [ 5 ].

1. The pre-autophagosomal structure organized by concerted functions of APG genes is essential for autophagosome formation. EMBO J. 20, 5971-81
2. Altered sensitivity to amiloride in cystic fibrosis. Observations using cultured sweat glands. Br J Clin Pharmacol 29, 227-34
3. Apg16p is required for the function of the Apg12p-Apg5p conjugate in the yeast autophagy pathway. EMBO J. 18, 3888-96
4. Apg5p functions in the sequestration step in the cytoplasm-to-vacuole targeting and macroautophagy pathways. Mol. Biol. Cell 11, 969-82
5. Structure of Atg5.Atg16, a complex essential for autophagy. J. Biol. Chem. 282, 6763-72