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Autophagy of glycogen (glycophagy) is crucial for the maintenance of cellular glucose homeostasis and physiology in mammals. STBD1 can serve as an autophagy receptor to mediate glycophagy by specifically recognizing glycogen and relevant key autophagic factors, but with poorly understood mechanisms. Here, we systematically characterize the interactions of STBD1 with glycogen and related saccharides, and determine the crystal structure of the STBD1 CBM20 domain with maltotetraose, uncovering a unique binding mode involving two different oligosaccharide-binding sites adopted by STBD1 CBM20 for recognizing glycogen. In addition, we demonstrate that the LC3-interacting region (LIR) motif of STBD1 can selectively bind to six mammalian ATG8 family members. We elucidate the detailed molecular mechanism underlying the selective interactions of STBD1 with ATG8 family proteins by solving the STBD1 LIR/GABARAPL1 complex structure. Importantly, our cell-based assays reveal that both the STBD1 LIR/GABARAPL1 interaction and the intact two oligosaccharide binding sites of STBD1 CBM20 are essential for the effective association of STBD1, GABARAPL1, and glycogen in cells. Finally, through mass spectrometry, biochemical, and structural modeling analyses, we unveil that STBD1 can directly bind to the Claw domain of RB1CC1 through its LIR, thereby recruiting the key autophagy initiation factor RB1CC1. In all, our findings provide mechanistic insights into the recognitions of glycogen, ATG8 family proteins, and RB1CC1 by STBD1 and shed light on the potential working mechanism of STBD1-mediated glycophagy. [ABSTRACT FROM AUTHOR]

In lecithotrophic larvae, egg yolk nutrients are essential for development. Although yolk proteins and lipids are the major nutrient sources for most animal embryos and larvae, the contribution of carbohydrates to development has been less understood. In this study, we assessed glucose and glycogen metabolism in developing Pacific abalone, a marine gastropod mollusc caught and cultured in east Asia. We found that glucose and glycogen content gradually elevated in developing abalone larvae, and coincident expression increases of gluconeogenic genes and glycogen synthase suggested abalone larvae had activated gluconeogenesis and glycogenesis during this stage. At settling, however, glycogen sharply decreased, with concomitant increases in glucose content and expression of Pyg and G6pc, suggesting the settling larvae had enhanced glycogen conversion to glucose. A liquid chromatography-mass spectrometry (LC/MS)-based metabolomic approach that detected intermediates of these pathways further supported active metabolism of glycogen. Immunofluorescence staining and in situ hybridization suggested the digestive gland has an important role as glycogen storage tissue during settlement, while many other tissues also showed a capacity to metabolize glycogen. Finally, inhibition of glycolysis affected survival of the settling veliger larvae, revealing that glucose is, indeed, an important nutrient source in settling larvae. Our results suggest glucose and glycogen are required for proper energy balance in developing abalone and especially impact survival during settling. [ABSTRACT FROM AUTHOR]

ABSTRACTPrion diseases like Creutzfeldt-Jakob disease in humans or scrapie in sheep and goats are infectious neurodegenerative diseases. Their infectious agent, called prion, is composed mainly of aggregated and misfolded prion protein and non-proteinaceous components. An example of such a common non-proteinaceous secondary component of natural prions is the polysaccharide scaffold. We studied the influence of such a polysaccharide on the conformational transition of PrP applying an in vitroconversion system. Here we report that glycogen supports and accelerates PrP amorphous aggregation similar to seeded aggregation and leads to co-aggregates. Furthermore, PrP fibril formation was highly accelerated in the presence of glycogen. [ABSTRACT FROM AUTHOR]

The molecular and cellular mechanisms behind glycogen metabolism and the energy metabolite translocation between mammal neurons and astrocytes have been well studied. A similar mechanism is proposed for rapid mobilization of local energy stores to support energy-dependent transepithelial ion transport in gills of the Mozambique tilapia (Oreochromis mossambicus). A novel gill glycogen phosphorylase isoform (tGPGG), which catalyzes the initial degradation of glycogen, was identified in branchial epithelial cells of O. mossambicus. Double in situ hybridization and immunocytochemistry demonstrated that tGPGG mRNA and glycogen were colocalized in glycogen-rich cells (GRCs), which surround ionocytes (labeled with a Na+-K+-ATPase antiserum) in gill epithelia. Concanavalin-A (a marker for the apical membrane) labeling indicated that GRCs and mitochondria-rich cells share the same apical opening. Quantitative real-time PCR analyses showed that tGPGG mRNA expression levels specifically responded to environmental salinity changes. Indeed, the glycogen content, glycogen phosphorylase (GP) protein level and total activity, and the density of tGPGG-expressing cells (i.e., GRCs) in fish acclimated to seawater (SW) were significantly higher than those in freshwater controls. Short-term acclimation to SW caused an evident depletion in the glycogen content of GRCs. Taken altogether, tGPGG expression in GRCs is stimulated by hyperosmotic challenge, and this may catalyze initial glycogen degradation to provide the adjacent ionocytes with energy to carry out iono- and osmoregulatory functions. [ABSTRACT FROM AUTHOR]