The phosphoglucose isomerase from the hyperthermophilic archaeon Pyrococcus furiosus is a unique glycolytic enzyme that belongs to the cupin superfamily

Pyrococcus furiosus uses a variant of the Embden-Meyerhof pathway during gr owth on sugars. All but one of the genes that encode the glycolytic enzymes of P. furiosus have previously been identified, either by homology searchi ng of its genome or by reversed genetics. We here report the isolation of t he missing link of the pyrococcal glycolysis, the phosphoglucose isomerase (PGI), which was purified to homogeneity from P. furiosus and biochemically characterized. The P. furiosus PGI, a dimer of identical 23.5-kDa subunits , catalyzes the reversible isomerization of glucose 6-phosphate to fructose 6-phosphate, with K, values of 1.99 and 0.63 mm, respectively. An optimum pH of 7.0 has been determined in both directions, and at its optimum temper ature of 90 degreesC the enzyme has a half-life of 2.4 h. The N-terminal se quence was used for the identification of the pgiA gene in the P. furiosus genome. The pgiA transcription start site has been determined, and a monoci stronic messenger was detected in P. furiosus during growth on maltose and pyruvate. The pgiA gene was functionally expressed in Escherichia coli BL21 (DE3). The deduced amino acid sequence of this first archaeal PGI revealed that it is not related to its bacterial and eukaryal counterparts. In contr ast, this archaeal PGI shares similarity with the cupin superfamily that co nsists of a variety of proteins that are generally involved in sugar metabo lism in both prokaryotes and eukaryotes. As for the P. furiosus PGI, distin ct phylogenetic origins have previously been reported for other enzymes fro m the pyrococcal glycolytic pathway. Apparently, convergent evolution by re cruitment of several unique enzymes has resulted in the unique Pyrococcus g lycolysis.