Unique Isoprenoid Biosynthesis Machinery of the Hyperthermophilic Archaea

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The isoprenoids constitute a large, diverse and important class of molecules that includes over 23,000 known members ncluding sterols, dolichols, carotenoids, sesquiterpenes, and quinones. Biologically derived isoprenoids form the basis of a broad spectrum of important health-related products including antitumor agents (taxol), antimicrobial agents (ipomeamarone and capsidiol), and food pigments (astaxanthin). However, since only low levels of isoprenoids or their slow accumulation over long periods typically are required for biological function in bacteria and eucarya, the corresponding enzymatic machinery is at low concentration and/or is characterized by low turnover number. The archaea necessarily have higher throughput isoprenoid biosynthesis machinery; as their membrane lipids are based solely on branched-chain, saturated hydrocarbons condensed with polyol (usually glycerol)-based headgroups. Most commonly, the lipid hydrocarbons are C2ophytanyl chains; and they are coupled to a glyceryl moiety through ether linkages as opposed to the less stable ester-linked membrane lipids of bacteria and eucarya. Many archaea, especially the hyperthermophiles, also contain isoprenoid lipids consisting of C4obiphytanyl chains coupled at both ends to polyols to give macrocyclic, bipolar tetraether lipids. The biochemistry of the isoprenoid ether-linked phospholipids of archaeal membranes, based typically on diphytanylglycerol diethers and dibiphytanyldiglycerol tetraethers, is unique to the archaeal domain; and the latter steps in tetraether-lipid biosynthesis entail unprecedented isoprenoid biochemistry. The chemical robustness of isoprenoid ether lipids as well as their ability to form more stable lipid membrane structures has led to a number of important emerging applications for these molecular species including usage in liposomes for drug delivery and reconstitution of membrane-bound protein systems, and in planar lipid films for biosensor applications. Elucidation of archaeal metabolic pathways for ether lipid synthesis and characterization of their novel enzymes therefore will provide new biosyntnetic tools for the synthesis of industrially useful isoprenoid ether lipids and for the expansion of accessible isoprenoid chemistry for wide-ranging commercial application. This project focuses on the isoprenoid biosynthetic machinery of an extremely thermophilic, heterotrophic sulfate-reducing archaeon, Archaeoglobus fulgidus, whose genome has been sequenced. The project entails the novel, coordinated application of biochemical research technology, i.e., extreme thermophile culture under varied conditions, protein purification and enzyme assays (including use of radiolabeling and of LC/MS), full-genome DMAmicroarrays, and gene cloning and expression, (1) to identify or to confirm hypothesized enzyme activities, (2) to assign DNA sequences to these enzymes, (3) to study their kinetics and regulation, (4) to gain insight into the metabolic capabilities of the originating organism, and (5) to explore the synthetic utility of the novel enzymes discovered. This project will uncover new biological routes for the synthesis of a complex class of molecules that includes potent anti-cancer and anti-microbial drugs. These molecules also may prove useful in the design of new drug delivery vehicles and of biosensors for health monitoring.