Ubiquitin-like modifier involved in intra-Golgi traffic. Modulates intra-Golgi transport through coupling between NSF activity and SNAREs activation. It first stimulates the ATPase activity of NSF which in turn stimulates the association with GOSR1 (By similarity). Involved in autophagy. Plays a role in mitophagy which contributes to regulate mitochondrial quantity and quality by eliminating the mitochondria to a basal level to fulfill cellular energy requirements and preventing excess ROS production. Whereas LC3s are involved in elongation of the phagophore membrane, the GABARAP/GATE-16 subfamily is essential for a later stage in autophagosome maturation (By similarity). Monomer. Interacts with ATG3, ATG7, ATG13 and ULK1. Interacts with TP53INP1 and TP53INP2. Interacts with TBC1D25. Directly interacts with SQSTM1 and BNIP3. Interacts with TECPR2 and PCM1. Interacts with TBC1D5. Interacts with TRIM5. Interacts with MEFV and TRIM21. Interacts with WDFY3. Interacts with UBA5; promoting recruitment of UBA5 to the endoplasmic reticulum membrane (By similarity). Interacts with GOSR1 (By similarity). Interacts with KBTBD6 AND KBTBD7; the interaction is direct (By similarity). 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, GABARAPL2-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, GABARAPL2-II. During non-canonical autophagy, the processed form is conjugated to phosphatidylserine (PS) phospholipid. ATG4 proteins also mediate the delipidation of PE-conjugated forms required for GABARAPL2 recycling when autophagosomes fuse with lysosomes. 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-87 and Ser-88 by TBK1 prevents interaction with ATG4 (ATG4A, ATG4B, ATG4C or ATG4D). Phosphorylation by TBK1 on autophagosomes prevents their delipidation by ATG4 and premature removal from nascent autophagosomes. Belongs to the ATG8 family.