Glycogen is the major mammalian glucose storage cache and is critical
April 9, 2017
Glycogen is the major mammalian glucose storage cache and is critical for energy homeostasis. rate of metabolism. Analyses of LD individual mutations define the mechanism by which subsets of mutations disrupt laforin function. These data provide fundamental insights linking glycogen rate of metabolism to neurodegenerative disease. Intro Glycogen the major glucose storage molecule in animals plays an essential part in energy rate of metabolism throughout the body. The brain is the organ most susceptible to decreases in glucose availability (Dinuzzo et al. 2014 Fryer and Brown 2014 During the past 20 years the perceived role of mind glycogen offers shifted from an emergency energy supply to a dynamic participant in mind rate of metabolism (Dinuzzo et al. 2014 Fryer and Brown 2014 Swanson 1992 While neuronal glycogen was thought to be limited to embryonic neurons adult neurons communicate both glycogen synthase and glycogen phosphorylase and they create low levels of glycogen (Duran et al. 2014 Lovatt et al. 2007 Pfeiffer-Guglielmi et al. 2003 Saez et SERK1 al. 2014 Vilchez et al. 2007 However glycogen synthesis in neurons must be tightly controlled because both over-accumulation and aberrant build up induce neuronal apoptosis (DePaoli-Roach et NVP-LAQ824 al. 2010 Duran et al. 2014 Turnbull et al. 2011 Valles-Ortega et al. 2011 Vilchez et al. 2007 Glycogen is definitely a branched polymer of glucose units became a member of by α-1 4 linkages created by glycogen synthase and branches happening every 12-14 models via α-1 6 branches produced by branching enzyme (Roach NVP-LAQ824 et al. 2012 Branches within glycogen are equally distributed resulting in a spherical structure with exposed non-reducing chain ends. This unique organization allows cells to store up to 55 0 glucose units inside a water-soluble form that can be rapidly released during bursts of metabolic energetics. Mutations in the (and (Gentry et al. 2007 Tagliabracci et al. 2008 Tagliabracci et al. 2007 Worby et al. 2006 Laforin possesses a carbohydrate binding module (CBM) family 20 website followed by a dual specificity phosphatase (DSP) website (Minassian et al. 1998 Serratosa et al. 1999 Wang et al. 2002 Highlighting its fundamental biological importance laforin orthologs are found in all vertebrates as well as several unicellular eukaryotes (Gentry et al. 2007 Gentry and Pace 2009 While having a critical part in normal glycogen rate of metabolism and aberrant LB formation the mechanism of glycogen dephosphorylation by laforin is not known. Further LD mutations are distributed throughout the primary sequence of laforin leaving open the crucial question of the mechanism(s) by which mutations in laforin lead to LB formation. Vegetation utilize a cyclic process of reversible phosphorylation by glucan dikinases and glucan phosphatases for efficient starch degradation (Metallic et al. 2014 Streb and Zeeman 2012 Phosphorylation of starch outer glucans results in solubilization thereby permitting degradation by starch hydrolyzing amylases and subsequent dephosphorylation from the glucan phosphatases Starch Extra 4 (SEX4) and Like Sex Four2 (LSF2). All known glucan phosphatases are users of the Protein Tyrosine Phosphatase (PTP) superfamily within the Dual-Specificity Phosphatases (DSPs) clade (Gentry et al. 2009 Gentry et al. 2007 Tonks 2006 The DSP website is an ~150 amino acid website that is <10% identical among the 65 human being DSPs. The heterogeneous DSPs all utilize a cysteine residue at the base of the active site within the conserved Cx5R catalytic motif to perform nucleophilic attack within the phosphorus atom of the substrate (Tonks 2006 Variations within the DSP website and NVP-LAQ824 active site allow for different members of the DSP family to specifically dephosphorylate proteinaceous substrates glucans lipids or nucleic acids (Moorhead et al. 2009 Tonks 2006 Each glucan phosphatase possesses unique features that enable it to bind and dephosphorylate phosphorylated glucans. We recently shown the molecular basis for flower glucan phosphatase function (Meekins et al. 2013 Meekins et al. 2014 Vander Kooi et al. 2010 SEX4 possesses a DSP and CBM website followed by a carboxy-terminal (CT)-motif. In SEX4 the DSP and CBM share an extensive interdomain interface that forms a continuous binding pocket to engage a hexasaccharide. Conversely LSF2 possesses only a DSP website and CT-motif and utilizes two Secondary Binding Sites (SBSs) to engage glucan substrates. Laforin possesses CBM and DSP domains in the reverse NVP-LAQ824 orientation as SEX4 it lacks a CT motif and it possesses a unique inter-domain linker.