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Category: Microbial Genetics and Molecular Biology; Environmental Microbiology
Lipids: Biosynthesis, Function, and Evolution, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815516/9781555813918_Chap15-1.gif /docserver/preview/fulltext/10.1128/9781555815516/9781555813918_Chap15-2.gifAbstract:
This chapter summarizes the different biosynthetic steps of isoprenoid ether lipid biosynthesis in archaea, describing the underlying enzymatic reactions that have been characterized. The evolution of this lipid biosynthesis apparatus in a variety of archaea is discussed. The effect of the environment on the nature of the lipids present in archaeal cell membranes is scrutinized in an attempt to link structure and function. Similar to other isoprenoids, archaeal lipid side chains are assembled from two universal precursors: isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). In archaea, geranylgeranyl diphosphate (GGPP) synthase can elongate DMAPP to obtain both farnesyl diphosphate (FPP) and GGPP, the latter being the isoprenyl forming the side chains of C20-C20 diether lipids. However, similar to the studies on partially saturated side chains, there is little experimental evidence on when these structures are formed during the process of archaeal lipid biosynthesis. The detection of CDP-archaeol synthase and archaetidylserine synthase activities in Methanothermobacter thermautotrophicus suggests that the biochemical steps for the addition of polar head groups on archaeal lipid precursors, might proceed in a manner analogous to fatty acid biosynthesis in bacteria. High-performance liquid chromotography (HPLC), in combination with electrospray mass spectrometry (ES-MS) was used to characterize the membrane phospholipids and glycolipids of halophilic archaea and the cold-adapted methanogen M. burtonii.
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Basic structure of glycerol diether isoprenoid lipids. The sugars or polar head groups that are frequently attached to the sn-1 position of the glycerol moiety in archaeal diether lipids are not shown.
Basic structure of glycerol tetraether isoprenoid lipids. GDGT (glycerol-diakyl-glycerol tetraether) can display a number of cyclic rings (0 to 8) in its alkyl core. In GTGT (glycerol-triakyl-glycerol tetraether), only two of the four phytanyl side chains from the precursor diether lipids are linked by a C—C bond. Although only the antiparallel configuration is shown for the two glycerols forming the backbone of the tetraether lipids, both isomers are likely to be found in archaeal cells ( 43 ). GDNT (glycerol-dialkyl-nonitol tetraether) versions of most GDGTs, where one of the glycerol moieties is replaced by nonitol, are also found in a variety of archaea. The sugars or polar head groups usually attached to the hydroxy of the glycerol moieties in archaeal lipids are not shown.
Pathways for the biosynthesis of archaeal glycerol ether isoprenoid lipids. Boxed “A” beside an enzyme name indicates that the enzyme is found in all archaea, and boxed “S” indicates that the enzyme is found in some archaea.
Phylogenetic analysis of the stereospecific enzymes involved in archaeal isoprenoid lipid biosynthesis. (A) sn-Glycerol-1-phosphate dehydrogenase (G1PDH) and related protein families; dehydroquinate synthase (DHQS), L-arabinose isomerase (AraM), glycerol dehydrogenase (GDH), alcohol dehydrogenase (ADH). (B) Geranylgeranylglyceryl phosphate synthase (GGGPS). (C) Digeranylgeranylglyceryl phosphate synthase (DGGGPS) and related protein families; Bacteriochlorophyll/chlorophyll synthase (BchG/ChlG), homogentisic acid geranylgeranyl transferase (HGGT), 1,4-dihydroxy 2-naphtoate octaprenyl-transferase (MenA), heme biosynthesis farnesyltransferase (CyoE/COX10), ubiquinone biosynthetic polyprenyl transferase (UbiA/COQ2). The trees presented are based on maximum likelihood amino acid distances under the minimum evolution model and were obtained using PROTDIST. Bootstrap values represent the consensus of 100 trees obtained from pseudo-replicates of the original dataset. Taxon names of archaea are highlighted in bold.
Distribution of lipid biosynthesis enzymes and core lipids in the Archaeaa