4y0g
From Proteopedia
beta2 carbohydrate binding module (CBM) of AMP-activated protein kinase (AMPK)
Structural highlights
Function[AAKB2_RAT] Non-catalytic subunit of AMP-activated protein kinase (AMPK), an energy sensor protein kinase that plays a key role in regulating cellular energy metabolism. In response to reduction of intracellular ATP levels, AMPK activates energy-producing pathways and inhibits energy-consuming processes: inhibits protein, carbohydrate and lipid biosynthesis, as well as cell growth and proliferation. AMPK acts via direct phosphorylation of metabolic enzymes, and by longer-term effects via phosphorylation of transcription regulators. Also acts as a regulator of cellular polarity by remodeling the actin cytoskeleton; probably by indirectly activating myosin. Beta non-catalytic subunit acts as a scaffold on which the AMPK complex assembles, via its C-terminus that bridges alpha (PRKAA1 or PRKAA2) and gamma subunits (PRKAG1, PRKAG2 or PRKAG3) (By similarity). Publication Abstract from PubMedAMPK-activated protein kinase (AMPK) is a alphabetagamma heterotrimer that is important in regulating energy metabolism in all eukaryotes. The beta-subunit exists in two isoforms (beta1 and beta2) and contains a carbohydrate binding module (CBM) that interacts with glycogen. The two CBM isoforms (beta1- and beta2-CBM) are near identical in sequence and structure, yet show differences in carbohydrate binding affinity. beta2-CBM binds linear carbohydrates with four-fold greater affinity than beta1-CBM and binds single alpha1,6-branched carbohydrates up to 30-fold tighter. To understand these affinity differences, especially for branched carbohydrates, we determined the NMR solution structure of beta2-CBM in complex with the single alpha1,6 branched carbohydrate glucosyl-beta-cyclodextrin (gBCD) which supported the dynamic nature of the binding site, but resonance broadening prevented defining where the alpha1,6 branch bound. We therefore solved the X-ray crystal structures of beta1- and beta2-CBM, in complex with gBCD, to 1.7 A and 2.0 A respectively. The additional threonine (Thr-101) of beta2-CBM expands the size of the surrounding loop, creating a pocket that accommodates the alpha1,6 branch. Hydrogen bonds are formed between the alpha1,6 branch and the backbone of Trp-99 and Lys-102 side chain of beta2-CBM. In contrast the alpha1,6 branch could not be observed in the beta1-CBM structure, suggesting that it does not form a specific interaction. The orientation of gBCD bound to beta1- and beta2-CBM is supported by thermodynamic and kinetic data obtained through isothermal titration calorimetry and NMR. These results suggest that AMPK containing the muscle specific beta2-isoform may therefore have greater affinity to partially degraded glycogen. Determinants of oligosaccharide specificity of the carbohydrate binding modules of AMP-activated protein kinase.,Mobbs JI, Koay A, Di Paolo A, Bieri M, Petrie EJ, Gorman MA, Doughty L, Parker MW, Stapleton D, Griffin MD, Gooley PR Biochem J. 2015 Mar 16. PMID:25774984[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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