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  • Title: Glycogen debranching enzyme association with beta-subunit regulates AMP-activated protein kinase activity.
    Author: Sakoda H, Fujishiro M, Fujio J, Shojima N, Ogihara T, Kushiyama A, Fukushima Y, Anai M, Ono H, Kikuchi M, Horike N, Viana AY, Uchijima Y, Kurihara H, Asano T.
    Journal: Am J Physiol Endocrinol Metab; 2005 Sep; 289(3):E474-81. PubMed ID: 15886229.
    Abstract:
    AMP-activated protein kinase (AMPK) regulates both glycogen and lipid metabolism functioning as an intracellular energy sensor. In this study, we identified a 160-kDa protein in mouse skeletal muscle lysate by using a glutathione-S-transferase (GST)-AMPK fusion protein pull-down assay. Mass spectrometry and a Mascot search revealed this protein to be a glycogen debranching enzyme (GDE). The association between AMPK and GDE was observed not only in the overexpression system but also endogenously. Next, we showed the beta1-subunit of AMPK to be responsible for the association with GDE. Furthermore, experiments using deletion mutants of the beta1-subunit of AMPK revealed amino acids 68-123 of the beta1-subunit to be sufficient for GDE binding. W100G and K128Q, both beta1-subunit mutants, are reportedly incapable of binding to glycogen, but both bound GDE, indicating that the association between AMPK and GDE does not involve glycogen. Rather, the AMPK-GDE association is likely to be direct. Overexpression of amino acids 68-123 of the beta1-subunit inhibited the association between endogenous AMPK and GDE. Although GDE activity was unaffected, basal phosphorylation and kinase activity of AMPK, as well as phosphorylation of acetyl-CoA carboxylase, were significantly increased. Thus it is likely that the AMPK-GDE association is a novel mechanism regulating AMPK activity and the resultant fatty acid oxidation and glucose uptake.
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