Seems to act as a glycogen-targeting subunit for PP1. PP1 is essential for cell division, and participates in the regulation of glycogen metabolism, muscle contractility and protein synthesis. Interacts with PPP1CC catalytic subunit of PP1, and associates with glycogen. Interacts with EPM2A; in the presence of NHLC1/malin the interaction leads to PPP1R3D ubiquitination and autophagic degradation. Expressed in all tissues tested. High expression in skeletal muscle and heart. The CBM21 domain is known to be involved in the localization to glycogen and is characteristic of some regulatory subunit of phosphatase complexes.