Multifunctional enzyme acting as 1,4-alpha-D-glucan:1,4-alpha-D-glucan 4-alpha-D-glycosyltransferase and amylo-1,6-glucosidase in glycogen degradation. Transfers a segment of a (1->4)-alpha-D-glucan to a new position in an acceptor, which may be glucose or a (1->4)-alpha-D-glucan. Hydrolysis of (1->6)-alpha-D-glucosidic branch linkages in glycogen phosphorylase limit dextrin. Monomer. Interacts with NHLRC1/malin (By similarity). Under glycogenolytic conditions localizes to the nucleus. Ubiquitous. Expressed in striated skeletal muscle, heart, liver, spleen, skin, spinal cord, lung, kidney and testicle. Ubiquitinated. Belongs to the glycogen debranching enzyme family.