The genetic and biochemical research of lipid biosynthesis in archaea

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1. We Succeeded in isolating the gene of hexaprenyl diphosphate synthase, which is considered to produce the precursor of the C30 side-chain of caldariellaquinone, from a thermoacidophilic archaeon Sulfolobus solfataticus based on homology searching from its whole-genomesequence. The gene was exogenously expressed in Escherichia coli, and the recombinant enzyme was purified and characterized. In consequence, it was proved to be the homomultimeric-type enzyme, which deffers from well-studied bacterial mudium-chain prenyl diphosphate synthases that have heterodimeric structures. Moreover, as the result of the phylogenetic analysis of the sequences of various prenyl diphosphate synthases, the archaeal enzyme was suggested to be closely related with eukaryotic short-chain enzymes, not with other medium-and long-chain enzymes; This idea was also supported by the result of a mutagenic study, in which partical sequences of prenyl diphosphate synthases from other organisms were site- derectedl … More y introduced in the srchaeal hexaprenyl diphosphate synthase.2. The gene of isopentenyl diphosphate isomerase was isolated from Sulfolobus shibatae and expressed in E. coli. This enzyme is important for biosynthesis of isoprenoid compounds in archaea because it catalyzes the first step of their biosynthetic pathways. The enzyme was proved to have novel properties; for axample, it shows co-enzyme requirement largely different with those of known isopentenyl hiphosphate synthases. Besides, the enzyme was suggested to have structural similarity with some types of oxidoreductases.3. We isolated the genes of various enzymes that catalyze the reactions of isoprenoid biosynthesis and proved their functions by expressing them in the cells of E. coli. The enzyme are thought to be valuable to investigate the evolutional route of each group of enzyes in which they are contained, because they have uniwue characteristics. For example, lycopene cyclase from S. solfataricus was proved to have the fusion-type structure specific for archaeal ones. Less