The semi-phosphorylative Entner-Doudoroff pathway in hyperthermophilic archaea: a re-evaluation.
Biochemical studies have suggested that, in hyperthermophilic archaea, the metabolic conversion of glucose via the ED (Entner-Doudoroff) pathway generally proceeds via a non-phosphorylative variant. A key enzyme of the non-phosphorylating ED pathway of Sulfolobus solfataricus, KDG (2-keto-3-deoxygluconate) aldolase, has been cloned and characterized previously. In the present study, a comparative genomics analysis is described that reveals conserved ED gene clusters in both Thermoproteus tenax and S. solfataricus. The corresponding ED proteins from both archaea have been expressed in Escherichia coli and their specificity has been identified, revealing: (i) a novel type of gluconate dehydratase (gad gene), (ii) a bifunctional 2-keto-3-deoxy-(6-phospho)-gluconate aldolase (kdgA gene), (iii) a 2-keto-3-deoxygluconate kinase (kdgK gene) and, in S. solfataricus, (iv) a GAPN (non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase; gapN gene). Extensive in vivo and in vitro enzymatic analyses indicate the operation of both the semi-phosphorylative and the non-phosphorylative ED pathway in T. tenax and S. solfataricus. The existence of this branched ED pathway is yet another example of the versatility and flexibility of the central carbohydrate metabolic pathways in the archaeal domain.
Ahmed
Hatim
H
Department of Microbiology, University Duisburg-Essen, Campus Essen, Universitätsstr. 5, 45117 Essen, Germany.
Ettema
Thijs J G
TJ
Tjaden
Britta
B
Geerling
Ans C M
AC
van der Oost
John
J
Siebers
Bettina
B
D000446:Aldehyde-Lyases / Q000235:genetics / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics / Q000378:metabolism; D006836:Hydro-Lyases / Q000235:genetics / Q000378:metabolism; D005810:Multigene Family / Q000235:genetics; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism; D016944:Sulfolobus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D041542:Thermoproteus / Q000201:enzymology* / Q000235:genetics
D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D017853:Phosphotransferases (Alcohol Group Acceptor); C020578:gluconokinase; D000446:Aldehyde-Lyases; C100131:phospho-2-keto-3-deoxy-gluconate aldolase; D006836:Hydro-Lyases; C020576:gluconate dehydratase