Ubiquitin tags glycogen and metabolites, reshaping our view of cellular catabolism

A new method, NoPro-clipping, reveals widespread ubiquitination of non-protein biomolecules in mammalian cells and tissues, notably glycogen (highest in liver and skeletal muscle) and endogenous glycerol and spermine. Glycogen ubiquitination can route glycogen to lysosomes and lower its levels, is altered in glycogen storage diseases, and increases in fasting liver, suggesting ubiquitin participates in physiological glycogen breakdown. The study broadens ubiquitin’s role from a protein modifier to a general modifier of biomolecules, with implications for metabolism and disease.