Functions as an E1 enzyme essential for multisubstrates such as GABARAPL1 and ATG12. Forms intermediate conjugates with GABARAPL1 (GABARAPL2, GABARAP or MAP1ALC3). Formation of the final GABARAPL1-PE conjugate is essential for autophagy. Subunit: Homodimer (By similarity). Interacts with ATG3 and ATG12. The complex, composed of ATG3 and ATG7, plays a role in the conjugation of ATG12 to ATG5. In yeast, ATG7 appears to be required for fusion of peroxisomal and vaculuolar membranes. Belongs to the ATG7 family.