Structural basis for 2′-phosphate incorporation into glycogen by glycogen synthase

Glycogen is a branched glucose polymer found in most animals, fungi, bacteria, and archaea as an osmotically neutral means of energy storage. Glycogen also contains minor amounts of phosphate which can be removed by a dual specificity phosphatase, laforin. Accumulation of phosphate results in highly insoluble glycogen deposits and underlies Lafora disease, a devastating form of myoclonus epilepsy. In this paper, we present structural and kinetic data that support a plausible mechanism by which phosphate is directly incorporated into glycogen by glycogen synthase.