Glyceraldehyde-3-Phosphate Ferredoxin Oxidoreductase fromMethanococcus maripaludis

Abstract

The genome sequence of the non-sugar-assimilating mesophile Methanococcus maripaludis contains three genes encoding enzymes: a nonphosphorylating NADP ؉ -dependent glyceraldehyde-3-phosphate dehydrogenase (GAPN), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and glyceraldehyde-3-phosphate ferredoxin oxidoreductase (GAPOR); all these enzymes are potentially capable of catalyzing glyceraldehyde-3-phosphate (G3P) metabolism. GAPOR, whose homologs have been found mainly in archaea, catalyzes the reduction of ferredoxin coupled with oxidation of G3P. GAPOR has previously been isolated and characterized only from a sugar-assimilating hyperthermophile, Pyrococcus furiosus (GAPOR Pf ), and contains the rare metal tungsten as an irreplaceable cofactor. Active recombinant M. maripaludis GAPOR (GAPOR Mm ) was purified from Escherichia coli grown in minimal medium containing 100 M sodium molybdate. In contrast, GAPOR Mm obtained from cells grown in medium containing tungsten (W) and W and molybdenum (Mo) or in medium without added W and Mo did not display any activity. Activity and transcript analysis of putative G3P-metabolizing enzymes and corresponding genes were performed with M. maripaludis cultured under autotrophic conditions in chemically defined medium. The activity of GAPOR Mm was constitutive throughout the culture period and exceeded that of GAPDH at all time points. As GAPDH activity was detected in only the gluconeogenic direction and GAPN activity was completely absent, only GAPOR Mm catalyzes oxidation of G3P in M. maripaludis. Recombinant GAPOR Mm is posttranscriptionally regulated as it exhibits pronounced and irreversible substrate inhibition and is completely inhibited by 1 M ATP. With support from flux balance analysis, it is concluded that the major physiological role of GAPOR Mm in M. maripaludis most likely involves only nonoptimal growth conditions.Glyceraldehyde-3-phosphate ferredoxin oxidoreductase (GAPOR) catalyzes a dual substrate electron-transfer reaction in which oxidation of glyceraldehyde-3-phosphate (G3P) yields 3-phosphoglycerate (3PG) concomitant with reduction of oxidized ferredoxin. GAPOR and its homologs are found mainly in archaea including both euryarchaeota and crenarcheaota and especially in hyperthermophiles (26,38,42). Homologs can also be found in draft sequences of deltaproteobacterial species (

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

“…A GAPDH operating in the catabolic direction in Archaea has been identified mainly in mesophilic haloarchaea and methanogens, with the exception of Mco. maripaludis, which also possesses a GAPOR (154). In mesophilic sugar-degrading halophiles, neither GAPN nor GAPOR activity could be detected, although a GAPN sequence homolog has been reported for Halobacterium NRC-1 (153).…”

“…maripaludis is the only mesophile that has been reported so far to possess GAPOR and classical GAPDH for GAP conversion (154). Expression studies indicate that the enzyme requires molybdenum (Mo) for activity and, as for other GAPORs, catalyzes only the glycolytic oxidation of GAP to 3PG.…”

“…However, Mco. maripaludis GAPOR was reported to contain molybdenum instead of tungsten (154). Although no crystal structure of a GAPOR itself is available, those of two members of the AOR enzyme family, the dimeric AOR and the tetrameric FOR from Pyr.…”

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

“…aerophilum, and Mco. maripaludis have been characterized in detail (41,154,156,(159)(160)(161). GAPORs represent ϳ65-to 70-kDa monomers and are highly specific for GAP as the substrate.…”