Note: a dashed line (without arrowheads) between two compound names is meant to imply that the two names are just different instantiations of the same compound -- i.e. one may be a specific name and the other a general name, or they may both represent the same compound in different stages of a polymerization-type pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
Synonyms: glycogen catabolism
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Sugars Biosynthesis|
|Degradation/Utilization/Assimilation → Carbohydrates Degradation → Polysaccharides Degradation → Glycogen Degradation|
|Degradation/Utilization/Assimilation → Polymeric Compounds Degradation → Polysaccharides Degradation → Glycogen Degradation|
In many bacteria including Escherichia coli glycogen is the primary carbon and energy storage compound. Evidence suggests that it may play a role in the long-term survival of the cell. In E. coli glycogen is stored in granules in the cytosol [AlonsoCasajus06]. It is biosynthesized in a highly regulated manner when carbon is plentiful, but other nutrients are limiting (see pathway glycogen biosynthesis I (from ADP-D-Glucose)). Glycogen is utilized when carbon sources become limiting. The regulation of endogenous glycogen metabolism in E. coli remains incompletely understood [Eydallin07, Montero09, Eydallin10, Montero10] and has been the subject of metabolic modeling studies [Park11, Yamamotoya12].
E. coli genes glgP and glgX are involved in glycogen degradation, whereas glgA, glgB and glgC are involved in glycogen biosynthesis. Earlier studies suggested that the glg genes for glycogen metabolism are clustered into two tandemly arranged operons, glgBX and glgCAP. However, more recent transcription studies in E. coli K-12 demonstrated that genes glgBXCAP are transcribed in a single transcriptional unit under the control of promoter sequences upstream of glgB. In addition, a promoter within glgC controls the expression of glgA and glgP. These transcription units are part of both the RelA and PhoP-PhoQ regulons [Montero10].
E. coli and Salmonella cannot grow on exogenous glycogen, starch, or pullulan), although they are able to grow on linear α-1,4-linked maltodextrins ranging in size from maltose to maltodextrins of up to about 20 glucose units in length (in Mayer and Boos [ECOSAL], see below).
About This Pathway
The glgP and glgX genes are involved in the initial breakdown of glycogen. During endogenous glycogen degradation, the glycogen phosphorylase product of gene glgP shortens the glycogen chains sequentially from their nonreducing end to produce a limit dextrin (also called a glycogen phosphorylase limit dextrin). Overexpression of glgP can decrease glycogen to undetectable levels, and the lowering of glycogen levels directly correlates with increases in the expression of glycogen phosphorylase activity. The debranching enzyme product of glgX removes α-1,6-linked branches that are a maximum of four glucosyl residues in length to produce a debranched limit dextrin (also called a debranched glycogen phosphorylase limit dextrin). It is therefore likely that GlgX releases maltotetraose from glycogen and also plays an important role in the production of maltotriose, an endogenous inducer of the maltose system (see below) [AlonsoCasajus06, Dauvillee05].
Further breakdown of the maltodextrin intermediates, maltotetraose, maltotriose and maltose involves the products of the maltose utilization genes malP, malZ and malQ. These genes are part of the maltose/maltodextrin regulon controlled by MalT, a transcriptional activator that is activated by maltotriose [Dippel05, AlonsoCasajus06, Lengsfeld09].
Maltodextrin phosphorylase encoded by malP phosphorylytically cleaves glucosyl residues from the nonreducing end of maltodextrins producing α-D-glucose-1-phosphate and a shortened maltodextrin. Maltotetraose is the smallest substrate, therefore the ultimate product of MalP action on a maltodextrin is the inducer maltotriose [AlonsoCasajus06, Dippel05]. α-D-glucose 1-phosphate is converted to α-D-glucose-6-phosphate by phosphoglucomutase encoded by gene pgm. α-D-glucose-6-phosphate can spontaneously convert to its β epimer and enter central metabolism as shown in the pathway link.
Maltodextrin glucosidase encoded by malZ can cleave α-D-glucose residues sequentially from the reducing end of maltodextrins, with the smallest substrate being maltotriose. In the case of maltotriose, the reaction products are α-D-glucose and maltose. The former compound is a source of glucose for the cell and can spontaneously epimerize to β-D-glucose (α-D-glucose ↔ β-D-glucose) and enter central metabolism as shown in the pathway link. Although MalZ is a maltodextrin-specific enzyme, its exact role is unclear and it is not essential for maltose or maltodextrin utilization [AlonsoCasajus06, Lengsfeld09].
Amylomaltase encoded by malQ is a 4-α-glucanotransferase that is essential for maltose degradation. MalQ mutants are unable to grow on maltose. Amylomaltase preferentially removes glucose from the reducing ends of maltose and small maltodextrins, transferring the enzyme-bound dextrinyl residue to the nonreducing ends of other maltodextrins, thereby forming longer maltodextrins (in [Park11]). In this process the number of glucosidic linkages remains constant. Therefore MalQ can both degrade and synthesize the inducer maltotriose, allowing induction when the bacteria are grown on maltodextrins [AlonsoCasajus06]. The β-D-glucose formed is phosphorylated by glucokinase and the resulting β-D-glucose-6-phosphate enters glycolysis.
Reviews: Mayer, C. and W. Boos (2005) Hexose/Pentose and Hexitol/Pentitol Metabolism, Module 3.4.1 in [ECOSAL], Preiss, J. (2009) Glycogen: Biosynthesis and Regulation, Module 4.7.4 in [ECOSAL] and [Wang11l, Schlegel02]
AlonsoCasajus06: Alonso-Casajus N, Dauvillee D, Viale AM, Munoz FJ, Baroja-Fernandez E, Moran-Zorzano MT, Eydallin G, Ball S, Pozueta-Romero J (2006). "Glycogen phosphorylase, the product of the glgP Gene, catalyzes glycogen breakdown by removing glucose units from the nonreducing ends in Escherichia coli." J Bacteriol 188(14);5266-72. PMID: 16816199
Dauvillee05: Dauvillee D, Kinderf IS, Li Z, Kosar-Hashemi B, Samuel MS, Rampling L, Ball S, Morell MK (2005). "Role of the Escherichia coli glgX gene in glycogen metabolism." J Bacteriol 187(4);1465-73. PMID: 15687211
Eydallin07: Eydallin G, Viale AM, Moran-Zorzano MT, Munoz FJ, Montero M, Baroja-Fernandez E, Pozueta-Romero J (2007). "Genome-wide screening of genes affecting glycogen metabolism in Escherichia coli K-12." FEBS Lett 581(16);2947-53. PMID: 17543954
Eydallin10: Eydallin G, Montero M, Almagro G, Sesma MT, Viale AM, Munoz FJ, Rahimpour M, Baroja-Fernandez E, Pozueta-Romero J (2010). "Genome-wide screening of genes whose enhanced expression affects glycogen accumulation in Escherichia coli." DNA Res 17(2);61-71. PMID: 20118147
Montero09: Montero M, Eydallin G, Viale AM, Almagro G, Munoz FJ, Rahimpour M, Sesma MT, Baroja-Fernandez E, Pozueta-Romero J (2009). "Escherichia coli glycogen metabolism is controlled by the PhoP-PhoQ regulatory system at submillimolar environmental Mg2+ concentrations, and is highly interconnected with a wide variety of cellular processes." Biochem J 424(1);129-41. PMID: 19702577
Montero10: Montero M, Almagro G, Eydallin G, Viale AM, Munoz FJ, Bahaji A, Li J, Rahimpour M, Baroja-Fernandez E, Pozueta-Romero J (2010). "Escherichia coli glycogen genes are organized in a single glgBXCAP transcriptional unit possessing an alternative suboperonic promoter within glgC that directs glgAP expression." Biochem J 433(1);107-17. PMID: 21029047
Park11: Park JT, Shim JH, Tran PL, Hong IH, Yong HU, Oktavina EF, Nguyen HD, Kim JW, Lee TS, Park SH, Boos W, Park KH (2011). "Role of maltose enzymes in glycogen synthesis by Escherichia coli." J Bacteriol 193(10);2517-26. PMID: 21421758
Yamamotoya12: Yamamotoya T, Dose H, Tian Z, Faure A, Toya Y, Honma M, Igarashi K, Nakahigashi K, Soga T, Mori H, Matsuno H (2012). "Glycogen is the primary source of glucose during the lag phase of E. coli proliferation." Biochim Biophys Acta 1824(12);1442-8. PMID: 22750467
Bartl99: Bartl F, Palm D, Schinzel R, Zundel G (1999). "Proton relay system in the active site of maltodextrinphosphorylase via hydrogen bonds with large proton polarizability: an FT-IR difference spectroscopy study." Eur Biophys J 28(3);200-7. PMID: 10232933
Becker94: Becker S, Palm D, Schinzel R (1994). "Dissecting differential binding in the forward and reverse reaction of Escherichia coli maltodextrin phosphorylase using 2-deoxyglucosyl substrates." J Biol Chem 269(4);2485-90. PMID: 7905479
Becker95: Becker S, Schnackerz KD, Schinzel R (1995). "A study of binary complexes of Escherichia coli maltodextrin phosphorylase: alpha-D-glucose 1-methylenephosphonate as a probe of pyridoxal 5'-phosphate-substrate interactions." Biochim Biophys Acta 1243(3);381-5. PMID: 7727513
Boeck96: Boeck B, Schinzel R (1996). "Purification and characterisation of an alpha-glucan phosphorylase from the thermophilic bacterium Thermus thermophilus." Eur J Biochem 239(1);150-5. PMID: 8706700
Brautaset98: Brautaset T, Petersen S, Valla S (1998). "An experimental study on carbon flow in Escherichia coli as a function of kinetic properties and expression levels of the enzyme phosphoglucomutase." Biotechnol Bioeng 58(2-3);299-302. PMID: 10191405
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Dippel05a: Dippel R, Bergmiller T, Bohm A, Boos W (2005). "The maltodextrin system of Escherichia coli: glycogen-derived endogenous induction and osmoregulation." J Bacteriol 187(24);8332-9. PMID: 16321937
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