Ubiquitin-like modifier that plays a role in intracellular transport of GABA(A) receptors and its interaction with the cytoskeleton. Involved in autophagy: 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. Also required for the local activation of the CUL3(KBTBD6/7) E3 ubiquitin ligase complex, regulating ubiquitination and degradation of TIAM1, a guanyl-nucleotide exchange factor (GEF) that activates RAC1 and downstream signal transduction. Thereby, regulates different biological processes including the organization of the cytoskeleton, cell migration and proliferation. Involved in apoptosis. Interacts with GPHN (PubMed:10900017). Interacts with NSF (By similarity). Interacts with ATG7 (PubMed:11890701). Interacts with ATG3 and ATG13 (By similarity). Interacts with alpha-tubulin (By similarity). Interacts with beta-tubulin (PubMed:10899939). Interacts with GABRG2 (By similarity). Interacts with RB1CC1 (By similarity). Interacts with ULK1 (By similarity). Interacts with CALR (By similarity). Interacts with DDX47 (By similarity). Interacts with TP53INP1 and TP53INP2 (By similarity). Interacts with TBC1D5 (By similarity). Interacts with TBC1D25 (PubMed:21383079). Directly interacts with SQSTM1 (By similarity). Interacts with MAPK15 (By similarity). Interacts with TECPR2 (By similarity). Interacts with PCM1 (By similarity). Interacts with TRIM5 and TRIM21 (By similarity). Interacts with MEFV (By similarity). Interacts with KIF21B (By similarity). Interacts with WDFY3; this interaction is required for WDFY3 recruitment to MAP1LC3B-positive p62/SQSTM1 bodies (By similarity). Interacts with FLCN; interaction regulates autophagy (By similarity). Interacts with UBA5 (By similarity). Interacts with KBTBD6 and KBTBD7; the interaction is direct and required for the ubiquitination of TIAM1 (By similarity). Largely associated with intracellular membrane structures including the Golgi apparatus and postsynaptic cisternae. Colocalizes with microtubules (PubMed:10899939). Localizes also to discrete punctae along the ciliary axoneme (PubMed:24089209). 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, GABARAP-I (PubMed:14530254). The processed form is then activated by APG7L/ATG7, transferred to ATG3 and conjugated to phosphatidylethanolamine (PE) phospholipid to form the membrane-bound form, GABARAP-II (By similarity). During non-canonical autophagy, the processed form is conjugated to phosphatidylserine (PS) phospholipid (By similarity). ATG4 proteins also mediate the delipidation of PE-conjugated forms (PubMed:33795848). In addition, ATG4B and ATG4D mediate delipidation of ATG8 proteins conjugated to PS during non-canonical autophagy (By similarity). ATG4B constitutes the major protein for proteolytic activation (By similarity). ATG4D is the main enzyme for delipidation activity (PubMed:33795848). Belongs to the ATG8 family.