Proteomic Analysis of Glycogen‐Bound Proteins

Maintenance and utilization of glycogen occurs through the concerted action of a defined group of enzymes. In addition, the glycogen particle is intimately connected with other metabolic pathways and targeted to specific loci within the cell. We hypothesize that the tight regulation and targeting of the glycogen particle requires the binding of other regulatory proteins to the particle, if only at a much lower stoichiometry compared to the glycogen metabolic enzymes. Using a series of centrifugation steps we isolated the glycogen pellet from liver tissue and 3T3‐L1 adipocyte cells. In each case about 1% of total cytosolic protein was associated with the glycogen pellet and formed reproducible banding patterns in SDS‐PAGE. The pellets were digested with trypsin and the resulting peptides identified through mass spectrometry. We have identified all known glycogen metabolic enzymes. In addition, novel glycogen associated proteins have been identified. These include: proteins from the endoplasmic reticulum, lysosomal associated membrane protein‐1, an autophagy protein which results in glycogen hyper¬accumulation when disrupted, 14‐3‐3 isoforms which regulate phosphoproteins, and genethonin‐1, a protein of unknown function which contains a starch binding domain. This approach promises to identify proteins that mediate novel aspects of glycogen metabolism and function. (NIH‐DK‐43526)