Ubiquitin-like modifier involved in formation of autophagosomal vacuoles (autophagosomes). While LC3s are involved in elongation of the phagophore membrane, the GABARAP/GATE-16 subfamily is essential for a later stage in autophagosome maturation. Through its interaction with the reticulophagy receptor TEX264, participates in the remodeling of subdomains of the endoplasmic reticulum into autophagosomes upon nutrient stress, which then fuse with lysosomes for endoplasmic reticulum turnover. 3 different light chains, LC1, LC2 and LC3, can associate with MAP1A and MAP1B proteins (By similarity). Interacts with TP53INP1 and TP53INP2. Directly interacts with SQSTM1; this interaction leads to MAP1LC3A recruitment to inclusion bodies containing polyubiquitinated protein aggregates and to inclusion body degradation by autophagy. Interacts with ATG13. Interacts with ULK1. Interacts with TBC1D5. Found in a complex with UBQLN1 and UBQLN2. Interacts with UBQLN4 (via STI1 1 and 2 domains). Interacts with UBQLN1 in the presence of UBQLN4. Interacts with TRIM5. Interacts with MEFV. Interacts with RETREG1, RETREG2 and RETREG3. Interacts with PICALM. Interacts with the reticulophagy receptor TEX264. Interacts with MOAP1 (via LIR motif) (By similarity). LC3-II binds to the autophagic membranes. The precursor molecule is cleaved by ATG4 (ATG4A, ATG4B, ATG4C or ATG4D) to expose the glycine at the C-terminus and form the cytosolic form, LC3-I. The processed form is then activated by APG7L/ATG7, transferred to ATG3 and conjugated to phosphatidylethanolamine (PE) phospholipid to form the membrane-bound form, LC3-II. During non-canonical autophagy, the processed form is conjugated to phosphatidylserine (PS) phospholipid. ATG4 proteins also mediate the delipidation of PE-conjugated forms. In addition, ATG4B and ATG4D mediate delipidation of ATG8 proteins conjugated to PS during non-canonical autophagy. ATG4B constitutes the major protein for proteolytic activation (By similarity). ATG4D is the main enzyme for delipidation activity (By similarity). Phosphorylation at Ser-12 by PKA inhibits conjugation to phosphatidylethanolamine (PE). Belongs to the ATG8 family.