This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Carbohydrates Degradation → Polysaccharides Degradation → Starch Degradation|
|Degradation/Utilization/Assimilation → Polymeric Compounds Degradation → Polysaccharides Degradation → Starch Degradation|
Expected Taxonomic Range: Archaea
Many organisms including bacteria, fungi, metazoa, and plants can degrade glucose polymers derived from starch or glycogen (see pathways starch degradation II, starch degradation I, glycogen degradation I and glycogen degradation II). Some hyperthermophilic archaea have also been shown to produce starch-degrading enzymes, and pathways for the utilization of starch and its derivatives, such as a cyclodextrin, a maltodextrin, and maltose have been proposed. These hyperthermophilic archaea can utilize starch and its degradation products as primary carbon sources during anaerobic growth. Thermostable starch-degrading enzymes produced by hyperthermophilic organisms are of industrial interest [Lee06c, Hashimoto01, Labes07, Labes01].
Pyrococcus furiosus DSM 3638 was shown to degrade starch mainly via maltodextrins in a pathway involving an extracellular amylopullulanase, a transporter, an intracellular 4-α-glucanotransferase, and a maltodextrin phosphorylase, as described below in About This Pathway ( [Lee06c] and in [Labes07]).
The sulfate-reducing archaeon Archaeoglobus fulgidus 7324 has been shown to degrade starch via a unique pathway involving cyclodextrin intermediates [Labes07, Labes01] (see pathway starch degradation III).
In the hyperthermophilic archaeon Thermococcus sp. B1001 evidence suggested a starch degradation pathway via formation of cyclodextrins from starch extracellularly by a cyclomaltodextrin glucanotransferase, transport of cyclodextrins into the cell, and their degradation by a cyclodextrinase to the end products maltose and α-D-glucopyranose ( [Hashimoto01] and in [Labes07]) (see pathway starch degradation IV).
Among bacteria Escherichia coli cannot utilize starch, but it can metabolize short, linear maltodextrins (see pathway glycogen degradation I). However the enterobacterium Klebsiella oxytoca M5al can utilize starch as a sole source of carbon and energy. Mutant analysis suggested that it metabolizes starch by two pathways. The first was a proposed maltose/maltodextrin pathway involving extracellular degradation of starch by pullulanase and the disproportionation activity of cyclodextrin glucanotransferase to form linear maltodextins. After transport into the cell they are degraded to β-D-glucopyranose and α-D-glucopyranose 1-phosphate by the products of malP, malQ and malZ. The second was a proposed cyclodextrin pathway involving extracellular conversion of starch to cyclodextrins (see a cyclodextrin) by cyclodextrin glucanotransferase, transport into the cell, linearization by cyclodextrinase (CymH) [Feederle96], and further catabolism as in the maltose/maltodextrin pathway [Fiedler96, Pajatsch98].
About This Pathway
The hyperthermophilic archaeon Pyrococcus furiosus DSM 3638 is an obligately anaerobic heterotroph that is able to utilize a variety of sugars as a primary carbon source. Its genome encodes many glycosyl hydrolases and transferases, the physiological function of which are unclear. Using global transcriptional profiling data and biochemical studies [Lee06c] have defined the pathway for starch metabolism in Pyrococcus furiosus DSM 3638. This pathway involves an amylopullulanase (PF1935*) acting extracellularly, and 4-α-glucanotransferase (PF0272), α-glucan/maltodextrin phosphorylase (maltodextrin phosphorylase) (PF1535) and phosphoglucomutase (PF0588) acting intracellularly. Although other candidates for starch degrading enzymes were annotated in the Pyrococcus furiosus DSM 3638 genome, they did not appear to be functionally involved in starch degradation ( [Lee06c] and in [Labes07]).
In this pathway starch is degraded extracellularly by amylopullulanase which has both pullulanase and α-amylase activity. Products of its α-amylase activity include maltodextrins (see a maltodextrin), maltose and D-glucose [Kang05a, Dong97]. Two active transporters Mal-II and Mal-I transport maltodextrins and maltose respectively, into the cell [Koning02]. A 4-α-glucanotransferase generates α-D-glucopyranose from maltose and maltodextrins. α-glucan/maltodextrin phosphorylase (maltodextrin phosphorylase) converts maltodextrins to α-D-glucopyranose 1-phosphate [Lee06c].
The α-D-glucopyranose and α-D-glucopyranose 1-phosphate produced in the pathway are proposed to enter the novel glycolytic pathway of this organism after conversion of the latter compound to α-D-glucose 6-phosphate by phosphoglucomutase (EC 126.96.36.199) [Lee06c]. In aqueous solution the epimers α-D-glucopyranose and β-D-glucopyranose spontaneously interconvert, forming an equilibrium mixture [Franks87]. Likewise, α-D-glucose 6-phosphate exists in equilibrium with its epimer β-D-glucose 6-phosphate. These reactions can also be enzyme-catalyzed. Whether the α, β, or both α and β epimers are used depends upon the anomeric specificity of the enzymes that utilize these compounds.
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Dong97: Dong G, Vieille C, Zeikus JG (1997). "Cloning, sequencing, and expression of the gene encoding amylopullulanase from Pyrococcus furiosus and biochemical characterization of the recombinant enzyme." Appl Environ Microbiol 63(9);3577-84. PMID: 9293009
Feederle96: Feederle R, Pajatsch M, Kremmer E, Bock A (1996). "Metabolism of cyclodextrins by Klebsiella oxytoca m5a1: purification and characterisation of a cytoplasmically located cyclodextrinase." Arch Microbiol 165(3);206-12. PMID: 8599539
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Labes01: Labes A, Schonheit P (2001). "Sugar utilization in the hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324: starch degradation to acetate and CO2 via a modified Embden-Meyerhof pathway and acetyl-CoA synthetase (ADP-forming)." Arch Microbiol 176(5);329-38. PMID: 11702074
Labes07: Labes A, Schonheit P (2007). "Unusual starch degradation pathway via cyclodextrins in the hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324." J Bacteriol 189(24);8901-13. PMID: 17921308
Lee06c: Lee HS, Shockley KR, Schut GJ, Conners SB, Montero CI, Johnson MR, Chou CJ, Bridger SL, Wigner N, Brehm SD, Jenney FE, Comfort DA, Kelly RM, Adams MW (2006). "Transcriptional and biochemical analysis of starch metabolism in the hyperthermophilic archaeon Pyrococcus furiosus." J Bacteriol 188(6);2115-25. PMID: 16513741
Pajatsch98: Pajatsch M, Gerhart M, Peist R, Horlacher R, Boos W, Bock A (1998). "The periplasmic cyclodextrin binding protein CymE from Klebsiella oxytoca and its role in maltodextrin and cyclodextrin transport." J Bacteriol 180(10);2630-5. PMID: 9573146
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Qian94: Qian N, Stanley GA, Hahn-Hagerdal B, Radstrom P (1994). "Purification and characterization of two phosphoglucomutases from Lactococcus lactis subsp. lactis and their regulation in maltose- and glucose-utilizing cells." J Bacteriol 176(17);5304-11. PMID: 8071206
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