The non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase (GAPN) of Sulfolobus solfataricus: a key-enzyme of the semi-phosphorylative branch of the Entner–Doudoroff pathway

Abstract

Archaea utilize a branched modification of the classical Entner-Doudoroff (ED) pathway for sugar degradation. The semi-phosphorylative branch merges at the level of glyceraldehyde 3-phosphate (GAP) with the lower common shunt of the Emden-Meyerhof-Parnas pathway. In Sulfolobus solfataricus two different GAP converting enzymes-classical phosphorylating GAP dehydrogenase (GAPDH) and the non-phosphorylating GAPDH (GAPN)-were identified. In Sulfolobales the GAPN encoding gene is found adjacent to the ED gene cluster suggesting a function in the regulation of the semi-phosphorylative ED branch. The biochemical characterization of the recombinant GAPN of S. solfataricus revealed that-like the well-characterized GAPN from Thermoproteus tenax-the enzyme of S. solfataricus exhibits allosteric properties. However, both enzymes show some unexpected differences in co-substrate specificity as well as regulatory fine-tuning, which seem to reflect an adaptation to the different lifestyles of both organisms. Phylogenetic analyses and database searches in Archaea indicated a preferred distribution of GAPN (and/or GAP oxidoreductase) in hyperthermophilic Archaea supporting the previously suggested role of GAPN in metabolic thermoadaptation. This work suggests an important role of GAPN in the regulation of carbon degradation via modifications of the EMP and the branched ED pathway in hyperthermophilic Archaea.Keywords Glyceraldehyde-3-phosphate Á Non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase Á GAPN Á Aldehyde dehydrogenase superfamily Á Branched Entner-Doudoroff pathway Á Carbohydrate metabolism Á Archaea Abbreviations EDEntner-Doudoroff sp Semi-phosphorylative np Non-phosphorylative EMP Embden-Meyerhof-Parnas G1P

Carbohydrate Metabolism in Archaea: Current Insights into Unusual Enzymes and Pathways and Their Regulation

“…Only mesophilic extreme halophiles growing at the expense of sugars rely on the GAPDH/PGK couple for GAP oxidation in the modified EMP and ED pathways utilized for fructose and glucose degradation, respectively (70,123,152). Also, in most methanogens, neither GAPOR nor GAPN has been identified, which might reflect the inability of most methanogenic species to degrade sugars (36,153). However, some methanogens have been described to use glycogen as a storage compound, thus requiring a GAP-oxidizing system.…”

“…jannaschii, and for Mco. maripaludis, GAPOR, in addition to GAPDH/PGK, has been characterized in detail (153,154). In addition, in Tpl.…”

“…In addition, in Tpl. acidophilum, initially thought to degrade glucose exclusively via the nonphosphorylative ED branch involving glyceraldehyde (GA) dehydrogenase (GADH) oxidizing nonphosphorylated GA instead of GAP, no GAPN or GAPOR homologs could be identified (153). However, an aldehyde dehydrogenase (ALDH) paralog, which might utilize GAP as the substrate, has been found in the genome (32).…”

Archaeal Aldehyde Dehydrogenase ST0064 fromSulfolobus tokodaii, a Paralog of Non-Phosphorylating Glyceraldehyde-3-phosphate Dehydrogenase, Is a Succinate Semialdehyde Dehydrogenase

“…1,2) In hyperthermophilic archaea, allosteric non-phosphorylating glyceraldehyde-3-phosphate (GAP) dehydrogenase (GAPN), a key enzyme in the glycolytic pathway, has been identified and characterized. [3][4][5][6] A remarkable feature of archaeal GAPNs is allosteric regulation by glucose 1-phosphate (G1P), an intermediate of glycogen metabolism and of maltodextrin uptake. 7) Besides heterotropic activation by G1P, GAPNs from Thermococcus kodakarensis and Sulfolobus tokodaii are homotropically activated by the substrate GAP.…”

“…An alignment of the amino acid sequences of ST0064 orthlogs with characterized archaeal GAPNs 4,5,13) is shown in Fig. 1.…”