Biosynthesis of characteristic lipid-core of archaea - Understanding for the adaptation of archaea to harsh environment and toward a new design for lipid molecules

Archaea live under harsh conditions such as low pH, high temperature, high salt conditions. The characteristic ether-lipid contributes to the tolerance of harsh living conditions. The biosynthetic studies of this characteristic lipid molecule provide a new insight for the adaptations of archaea for the extreme environment, and provide a design of new lipid molecules useful for drug delivery systems. At first, the biosynthetic studies of the isoprenoidal portion of halophilic archaea were performed. It reveals the isoprenoidal portion of halophlies is made from acetate and C-4 unit derived from amino acid such as lysine. Next, the biosynthetic study of calditol, the hydrophilic portion of Sulfolobus lipid-core that consists of 5-memberd carbocycle bound to glycerol with ether-linkage, was presented. The carbocycle of calditol is biosynthesized from glucose with C-C bond formation of C 1 and C 5. It may involve the "cyclase" enzyme of the calditol carbocycles with broad substrate specificity that can be seen at the central metabolism of thermophilic archaea.