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Mol Cell. 2011 Nov 4;44(3):451-61. doi: 10.1016/j.molcel.2011.08.034.

Atg8 transfer from Atg7 to Atg3: a distinctive E1-E2 architecture and mechanism in the autophagy pathway.

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1
Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.

Abstract

Atg7 is a noncanonical, homodimeric E1 enzyme that interacts with the noncanonical E2 enzyme, Atg3, to mediate conjugation of the ubiquitin-like protein (UBL) Atg8 during autophagy. Here we report that the unique N-terminal domain of Atg7 (Atg7(NTD)) recruits a unique "flexible region" from Atg3 (Atg3(FR)). The structure of an Atg7(NTD)-Atg3(FR) complex reveals hydrophobic residues from Atg3 engaging a conserved groove in Atg7, important for Atg8 conjugation. We also report the structure of the homodimeric Atg7 C-terminal domain, which is homologous to canonical E1s and bacterial antecedents. The structures, SAXS, and crosslinking data allow modeling of a full-length, dimeric (Atg7~Atg8-Atg3)(2) complex. The model and biochemical data provide a rationale for Atg7 dimerization: Atg8 is transferred in trans from the catalytic cysteine of one Atg7 protomer to Atg3 bound to the N-terminal domain of the opposite Atg7 protomer within the homodimer. The studies reveal a distinctive E1~UBL-E2 architecture for enzymes mediating autophagy.

PMID:
22055190
PMCID:
PMC3277881
DOI:
10.1016/j.molcel.2011.08.034
[Indexed for MEDLINE]
Free PMC Article

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