earticle

영어

I will present our recent findings on the pathways and their regulation involved in central carbon metabolism in the hyperthermophilic archaeon, Thermococcus kodakaraensis KOD1. The entire genome sequence of this archaeon has been determined (1) and gene disruption systems have been developed (2). A whole genome DNA microarray is also available for transcriptome studies. T. kodakaraensis can utilize a variety of organic compounds for growth, which include poly(oligo)saccharides, peptides, amino acids and pyruvate (3). This archaeon utilizes the modified Embden-Meyerhof pathway for glycolysis, and we have examined the enzymes involved in the conversion of glyceraldehyde 3-phosphate to 3-phosphoglycerate, and phosphoenolpyruvate to pyruvate (4). In terms of gluconeogenesis, we have performed a biochemical and genetic analysis on the key enzyme fructose-1,6-bisphosphatase (5). Enzymes involved in the production of glycogen have also been identified (6), as well as a novel degradation pathway for chitin (7). T. kodakaraensis does not harbor a complete set of genes corresponding to the pentose phosphate pathway, necessary for pentose and nucleotide synthesis in bacteria and eukaryotes. We instead found that a reverse flux of the ribulose monophosphate pathway is responsible for pentose synthesis in this organism (8). Through investigations on the physiological role of Type III Rubiscos (9), we have identified a novel pathway that may be involved in retrieving excess pentose carbon and redirecting it back to glycolysis (10). In terms of amino acid metabolism, a variety of aminotransferase and 2-oxo acid:ferredoxin oxidoreductase homologs are present on the T. kodakaraensis genome. In search of (ADP-forming) acyl-CoA synthetases that should function in further breakdown of amino acids, we found that the five acetyl-CoA synthetase paralogs present on the genome encode acyl-CoA synthetases with distinct substrate specificities (11). A fruitful collaboration has also led to the identification of the regulator that is responsible for controlling glycolytic and gluconeogenic modes of growth in T. kodakaraensis (12).