Is Glycogenin Essential for Glycogen Synthesis? Anders Oldfors  Cell Metabolism  Volume 26, Issue 1, Pages 12-14 (July 2017) DOI: 10.1016/j.cmet.2017.06.017 Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 Function of Glycogenin in Normal Glycogen Synthesis and Muscle Glycogen Storage in Glycogenin-1 Deficiency in Humans (A) Synthesis of glycogen in human muscle. Dimers of glycogenin-1 catalyze two auto-glucosylation reactions using UDP-glucose (UDPG) as donor. A glucose-O-tyrosine linkage is formed at tyrosine 195, and then several α1,4-glucosidic linkages are formed to produce an oligosaccharide containing ∼8–13 glucose residues. The priming oligosaccharide chain is elongated by glycogen synthase, and the α-1,6 branching points are introduced by branching enzyme to form soluble glycogen granules. Each glycogen granule is ∼20 nm in diameter. (B) Biopsy of skeletal muscle in a patient with muscle weakness due to glycogenin-1 deficiency. Periodic acid and Schiff (PAS) staining to demonstrate polysaccharides shows deposition of PAS-positive material in fibers depleted of normal intermyofibrillar glycogen as well as in fibers with normal glycogen content apart from the inclusions (arrows). Many fibers show apparently normal glycogen content and distribution (arrowhead). (A) and (B) are modified and reprinted from Hedberg-Oldfors and Oldfors (2015), with permission from Elsevier. (C) Electron micrograph of the storage material illustrated in (B). The accumulated glycogen is less homogeneous in size and shape than normal muscle glycogen (illustrated in D), and some of the storage material has a fibrillar structure (arrowheads). (D) Normal human muscle glycogen adjacent to a mitochondrion (M) and a myofibril (MF). Cell Metabolism 2017 26, 12-14DOI: (10.1016/j.cmet.2017.06.017) Copyright © 2017 Elsevier Inc. Terms and Conditions