Metabolic pathway promiscuity in the archaeon Sulfolobus solfataricus revealed by studies on glucose dehydrogenase and 2-keto-3-deoxygluconate aldolase.
The hyperthermophilic Archaeon Sulfolobus solfataricus metabolizes glucose by a non-phosphorylative variant of the Entner-Doudoroff pathway. In this pathway glucose dehydrogenase and gluconate dehydratase catalyze the oxidation of glucose to gluconate and the subsequent dehydration of gluconate to 2-keto-3-deoxygluconate. 2-Keto-3-deoxygluconate (KDG) aldolase then catalyzes the cleavage of 2-keto-3-deoxygluconate to glyceraldehyde and pyruvate. The gene encoding glucose dehydrogenase has been cloned and expressed in Escherichia coli to give a fully active enzyme, with properties indistinguishable from the enzyme purified from S. solfataricus cells. Kinetic analysis revealed the enzyme to have a high catalytic efficiency for both glucose and galactose. KDG aldolase from S. solfataricus has previously been cloned and expressed in E. coli. In the current work its stereoselectivity was investigated by aldol condensation reactions between D-glyceraldehyde and pyruvate; this revealed the enzyme to have an unexpected lack of facial selectivity, yielding approximately equal quantities of 2-keto-3-deoxygluconate and 2-keto-3-deoxygalactonate. The KDG aldolase-catalyzed cleavage reaction was also investigated, and a comparable catalytic efficiency was observed with both compounds. Our evidence suggests that the same enzymes are responsible for the catabolism of both glucose and galactose in this Archaeon. The physiological and evolutionary implications of this observation are discussed in terms of catalytic and metabolic promiscuity.
Lamble
Henry J
HJ
Centre for Extremophile Research, the Department of Biology and Biochemistry, University of Bath, United Kingdom.
Heyer
Narinder I
NI
Bull
Steven D
SD
Hough
David W
DW
Danson
Michael J
MJ
D000446:Aldehyde-Lyases / Q000737:chemistry*; D000595:Amino Acid Sequence; D001483:Base Sequence; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology; D005690:Galactose / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D042843:Glucose 1-Dehydrogenase; D005948:Glucose Dehydrogenases / Q000737:chemistry*; D005985:Glyceraldehyde / Q000737:chemistry; D007700:Kinetics; D008954:Models, Biological; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D019289:Pyruvic Acid / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D017422:Sequence Analysis, DNA; D013379:Substrate Specificity; D016944:Sulfolobus / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
D011994:Recombinant Proteins; D005985:Glyceraldehyde; D019289:Pyruvic Acid; D005948:Glucose Dehydrogenases; D042843:Glucose 1-Dehydrogenase; C021470:2-keto-3-deoxygluconate aldolase; D000446:Aldehyde-Lyases; D005947:Glucose; D010100:Oxygen; D005690:Galactose