Biology subjects

Tourte, M.

Publications and source records attributed to Tourte, M..

3 recordsLinked to original sources

bioRxiv2023

Archaeal self-activating GPN-loop GTPases involve a lock-switch-rock mechanism for GTP hydrolysis

Three GPN-loop GTPases, GPN1-GPN3, are central to the maturation and trafficking of eukaryotic RNA polymerase II. This GTPase family is widely represented in archaea but typically occurs as single paralogs. Structural analysis of the GTP- and GDP-bound states of the Sulfolobus acidocaldarius GPN enzyme (SaGPN) showed that this central GPN-loop GTPase adopts two distinct quaternary structures. In the GTP-bound form the {gamma}-phosphate induces a tensed dimeric arrangement by interacting with the GPN region that is relaxed upon hydrolysis to GDP. Consequently, a rocking-like motion of the two protomers causes a major allosteric structural change towards the roof-like helices. Using a lock-switch-rock (LSR) mechanism, homo- and heterodimeric GPN-like GTPases are locked in the GTP-bound state and undergo large conformational changes upon GTP hydrolysis. A{Delta} saGPN strain of S. acidocaldarius was characterized by impaired motility and major changes in the proteome underscoring its functional relevance for S. acidocaldarius in vivo. Significance StatementGPN-loop GTPases have been found to be crucial for eukaryotic RNA polymerase II assembly and nuclear trafficking. Despite their ubiquitous occurrence in eukaryotes and archaea the mechanism by which these self-activating GTPases mediate their function is unknown. Our study on an archaeal representative from Sulfolobus acidocaldarius showed that these dimeric GTPases undergo large-scale conformational changes upon GTP hydrolysis, which can be summarized as a lock-switch-rock mechanism. The observed requirement of SaGPN for motility appears to be due to its large footprint on the archaeal proteome.

biochemistry↗

bioRxiv2021

The exploration of Thermococcus barophilus lipidome reveals the widest variety of phosphoglycolipids in Thermococcales.

One of the most distinctive characteristics of Archaea is their unique lipids. While the general nature of archaeal lipids has been linked to their tolerance to extreme conditions, little is known about the diversity of lipidic structures Archaea are able to synthesize, which hinders the elucidation of the physicochemical properties of their cell membrane. In an effort to widen the known lipid repertoire of the piezophilic and hyperthermophilic model archaeon Thermococcus barophilus, we comprehensively characterized its intact polar lipid (IPL), core lipid (CL), and polar head group compositions using a combination of cutting-edge liquid chromatography and mass spectrometric ionization systems. We tentatively identified 82 different IPLs based on five distinct CLs and 10 polar head group derivatives of phosphatidylhexoses, including compounds reported here for the first time, e.g., di-N-acetylhexosamine phosphatidylhexose-bearing lipids. Despite having extended the knowledge on the lipidome, our results also indicate that the majority of T. barophilus lipids remain inaccessible to current analytical procedures and that improvements in lipid extraction and analysis are still required. This expanded yet incomplete lipidome nonetheless opens new avenues for understanding the physiology, physicochemical properties, and organization of the membrane in this archaeon as well as other Archaea.

microbiology↗

bioRxiv2021

Membrane adaptation in the hyperthermophilic archaeon Pyrococcus furiosus relies upon a novel strategy involving glycerol monoalkyl glycerol tetraether lipids

Microbes preserve membrane functionality under fluctuating environmental conditions by modulating their membrane lipid composition. Although several studies have documented membrane adaptations in Archaea, the influence of most biotic and abiotic factors on archaeal lipid compositions remains underexplored. Here, we studied the influence of temperature, pH, salinity, the presence/absence of elemental sulfur, the carbon source, and the genetic background on the core lipid composition of the hyperthermophilic neutrophilic marine archaeon Pyrococcus furiosus. Every growth parameter tested affected the core lipid composition to some extent, the carbon source and the genetic background having the greatest influence. Surprisingly, P. furiosus appeared to only marginally rely on the two major responses implemented by Archaea, i.e., the regulation of the ratio of diether to tetraether lipids and that of the number of cyclopentane rings in tetraethers. Instead, this species increased the ratio of glycerol monoalkyl glycerol tetraethers (GMGT, aka. H-shaped tetraethers) to glycerol dialkyl glycerol tetrathers (GDGT) in response to decreasing temperature and pH and increasing salinity, thus providing for the first time evidence of adaptive functions for GMGT. Besides P. furiosus, numerous other species synthesize significant proportions of GMGT, which suggests that this unprecedented adaptive strategy might be common in Archaea. Significance statementWe describe here the membrane adaptive strategies the hyperthermophilic, neutrophilic, and marine model archaeon Pyrococcus furiosus implements in response to one of the largest sets of environmental stressors tested to date, including temperature, pH, salinity, presence/absence of elemental sulfur, carbon source, and genetic background. In contrast to the other archaea investigated so far, which response mainly involves the modulation of their diether/tetraether ratio and/or of their average number of cyclopentane rings, P. furiosus regulates its monoalkyl (so called H-shaped) to dialkyl tetraether ratio. Our study thus provides for the first time evidence of adaptive functions of archaeal monoalkyl tetraethers towards low temperature and pH and high salinity.

microbiology↗