Analysis of Enzymes in a Modified Embden Meyerhof Pathway of Hyperthermophilic Archaea and a Novel ATP Regeneration System

Abstract

Hyperthermophiles, a group of microorganisms whose optimum growth temperatures are above 80℃, have been isolated mainly from marine and continental volcanic environments. They are viewed as potential sources of extraordinarily stable biomolecules with applications in novel industrial processes. Most hyperthermophiles belong to the domain Archaea, the third domain of life, and are considered to be the most ancient of all extant life forms. Recent studies have revealed unusual energy metabolic processes in hyperthermophilic archaea, e.g. a modified Embden-Meyerhof pathway, that have not been observed so far in organisms belonging to the Bacteria and Eucarya domains. Several novel enzymes, e.g. ADP-dependent glucokinase and ADP-dependent phosphofructokinase, have been found to be involved in the modified Embden-Meyerhof pathway of the hyperthermophilic archaeon Pyrococcu furiosus. We cloned and sequenced the genes encoding the ADP-dependent glucokinases from P.furiosus and Thermococcus litoralis, a near relative of Pfuriosus. Their amino acid sequences did not show similarity with any ATP-dependent kinases that have been reported so far. On the other hand, the amino acid sequence of the P.furiosus enzyme showed a high degree of similarity (50%) with that renorted for the P.furiosus ADP-dependent phosphofructokinase. This suggests that these ADP-dependent kinases belong to a novel kinase family and might have evolved from a common origin. Recently, we have found that a novel bifunctional ADP-dependent glucokinase/phosphofructokinase is present in the hyperthermophilic archaeon Methanococcus jannaschii. The enzyme was proposed to be a common origin of the ADP-dependent glucokinase and phosphofructokinase from genome analysis. From an energy metabolic point of view, we have analyzed ATP-generation system in the P.furiosus glucogenesis and revealed that a novel regulation site for energy metabolism and a unique mode of ATP regeneration exist in the pathway of P.furiosus. The metabolic design observed in this microorganism might reflect the situation at an early stage of evolution. This review focuses mainly on the unique energy metabolism and related enzymes of P.furiosus and near relatives that have recently been observed.