E3 ubiquitin-protein ligase. Together with the phosphatase EPM2A/laforin, appears to be involved in the clearance of toxic polyglucosan and protein aggregates via multiple pathways. In complex with EPM2A/laforin and HSP70, suppresses the cellular toxicity of misfolded proteins by promoting their degradation through the ubiquitin-proteasome system (UPS). Ubiquitinates the glycogen-targeting protein phosphatase subunits PPP1R3C/PTG and PPP1R3D in a laforin-dependent manner and targets them for proteasome-dependent degradation, thus decreasing glycogen accumulation. Polyubiquitinates EPM2A/laforin and ubiquitinates AGL and targets them for proteasome-dependent degradation. Also promotes proteasome-independent protein degradation through the macroautophagy pathway. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with AGL. Interacts (via the NHL repeats) with EPM2A/laforin. Forms a complex with EPM2A/laforin and HSP70. Interacts with PRDM8 (PubMed:22961547). Localizes at the endoplasmic reticulum and, to a lesser extent, in the nucleus. Expressed in brain, cerebellum, spinal cord, medulla, heart, liver, skeletal muscle and pancreas. The RING domain is essential for ubiquitin E3 ligase activity. The disease is caused by variants affecting the gene represented in this entry.