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Biosynthesis of membrane-spanning lipids in Thermoanaerobacter ethanolicus and Thermotoga maritima

ABSTRACT: This SuperSeries is composed of the SubSeries listed below.

ORGANISM(S): Thermoanaerobacter ethanolicus Thermotoga maritima

PROVIDER: GSE211548 | GEO | 2022/10/26

REPOSITORIES: GEO

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Project description:Membrane-spanning lipids are present in a wide variety of archaea, but they are rarely in bacteria. Nevertheless, the (hyper)thermophilic members of the order Thermotogales harbor tetraester, tetraether, and mixed ether/ester membrane-spanning lipids mostly composed of core lipids derived from diabolic acids, C30, C32, and C34 dicarboxylic acids with two adjacent mid-chain methyl substituents. Lipid analysis of Thermotoga maritima across growth phases revealed a decrease of the relative abundance of fatty acids together with an increase of diabolic acids with independence of growth temperature. We also identified isomers of C30 and C32 diabolic acids, i.e., dicarboxylic acids with only one methyl group at C-15. Their distribution suggests they are products of the condensation reaction but are preferably produced when the length of the acyl chains is not optimal. Compared with growth at the optimal temperature of 80°C, an increase of glycerol ether-derived lipids was observed at 55°C. Our analysis only detected diabolic acid-containing intact polar lipids with phosphoglycerol (PG) head groups. Considering these findings, we hypothesize a biosynthetic pathway for the synthesis of membrane-spanning lipids based on PG polar lipid formation, suggesting that the protein catalyzing this process is a membrane protein. We also identified, by genomic and protein domain analyses, a gene coding for a putative plasmalogen synthase homologue in T. maritima that is also present in other bacteria producing sn-1-alkyl ether lipids but not plasmalogens, suggesting it is involved in the conversion of the ester-to-ether bond in the diabolic acids bound in membrane-spanning lipids. IMPORTANCE Membrane-spanning lipids are unique compounds found in most archaeal membranes, but they are also present in specific bacterial groups like the Thermotogales. The synthesis and physiological role of membrane-spanning lipids in bacteria represent an evolutionary and biochemical open question that points to the differentiation of the membrane lipid composition. Understanding the formation of membrane-spanning lipids is crucial to solving this question and identifying the enzymatic and biochemical mechanism performing this procedure. In the present work, we found changes at the core lipid level, and we propose that the growth phase drives the biosynthesis of these lipids rather than temperature. Our results identified physiological conditions influencing the membrane-spanning lipid biosynthetic process, which can further clarify the pathway leading to the biosynthesis of these compounds.

Project description:UnlabelledRegulation of coenzyme A (CoA) biosynthesis in bacteria and eukaryotes occurs through feedback inhibition targeting type I and type II pantothenate kinase (PanK), respectively. In contrast, the activity of type III PanK is not affected by CoA. As the hyperthermophilic bacterium Thermotoga maritima harbors only a single type III PanK (Tm-PanK), here we examined the mechanisms that regulate CoA biosynthesis in this organism. We first examined the enzyme responsible for the ketopantoate reductase (KPR) reaction, which is the target of feedback inhibition in archaea. A classical KPR homolog was not present on the T. maritima genome, but we found a homolog (TM0550) of the ketol-acid reductoisomerase (KARI) from Corynebacterium glutamicum, which exhibits KPR activity. The purified TM0550 protein displayed both KPR and KARI activities and was designated Tm-KPR/KARI. When T. maritima cell extract was subjected to anion-exchange chromatography, the fractions containing high levels of KPR activity also displayed positive signals in a Western blot analysis using polyclonal anti-TM0550 protein antisera, strongly suggesting that Tm-KPR/KARI was the major source of KPR activity in the organism. The KPR activity of Tm-KPR/KARI was not inhibited in the presence of CoA. We thus examined the properties of Tm-PanK and the pantothenate synthetase (Tm-PS) of this organism. Tm-PS was not affected by CoA. Surprisingly however, Tm-PanK was inhibited by CoA, with almost complete inhibition in the presence of 400 μM CoA. Our results suggest that CoA biosynthesis in T. maritima is regulated by feedback inhibition targeting PanK, although Tm-PanK is a type III enzyme.ImportanceBacteria and eukaryotes regulate the biosynthesis of coenzyme A (CoA) by feedback inhibition targeting type I or type II pantothenate kinase (PanK). The hyperthermophilic bacterium Thermotoga maritima harbors a single type III PanK (Tm-PanK), previously considered to be unaffected by CoA. By examining the properties of three enzymes involved in CoA biosynthesis in this organism, we found that Tm-PanK, although a type III enzyme, is inhibited by CoA. The results provide a feasible explanation of how CoA biosynthesis is regulated in T. maritima, which may also apply for other bacteria that harbor only type III PanK enzymes.

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Biosynthesis of membrane-spanning lipids in Thermoanaerobacter ethanolicus and Thermotoga maritima

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