Biology subjects

Maslac, N.

Publications and source records attributed to Maslac, N..

6 recordsLinked to original sources

bioRxiv2026

Emergence of histone-based chromatin complexity in Asgard archaea

The emergence of the eukaryotes coincided with the diversification of histone proteins and their post-translational modifications by enzymes that constitute the core of eukaryotic chromatin. Yet the evolutionary origins of this regulatory machinery are unknown. Here, we show that the key molecular components of histone-based chromatin regulation are present in the Asgard archaea, the closest prokaryotic relatives of eukaryotes. Asgard histones are abundant and have extended N-terminal tails rich in lysine residues that can be post-translationally modified, all of which are features shared with eukaryotic histones. In line with these findings, we identify enzymes from Asgard archaea that deposit or remove lysine acetylation on histone tails in vitro. Moreover, Asgard sirtuin deacetylases (SIR2 proteins) restore chromatin silencing in yeast, demonstrating the functional compatibility of Asgard enzymes with eukaryotic histone substrates. Our findings establish that the foundations of histone-based chromatin predate eukaryogenesis and place Asgard archaea as an evolutionary intermediate in the emergence of eukaryotic chromatin.

evolutionary biology↗

bioRxiv2026

Active virus-host system in a Lokiarchaeon culture

Asgard archaea are considered the closest prokaryotic relatives of eukaryotes and having a crucial role in eukaryogenesis. Only few organisms have been cultivated from this group and their viruses were previously described only through metagenomic reconstructions. Here, we report the first successful cultivation of an Asgard archaeal virus infecting a novel strain of Ca. Lokiarchaeum ossiferum B36. The 16 kbp integrated provirus is capable to excise and replicate independently leading to the formation of virus particles. Network analysis of shared protein clusters with other archaeal viruses places it in a new family, Fylgjaviridae. The host encodes a distinctive repertoire of antiviral defense systems, including Septu, Wadjet, and type II CBASS system, all different from the defense systems of the related strain Ca. L. ossiferum B35. Our cultures provide the first opportunity to study interactions of a virus-host system in Asgards and hold significant potential for developing genetic tools.

microbiology↗

bioRxiv2025

Molecular mechanism of nitrogenase sequestration by a PII-protein couple

The microbial process of N2-fixation is crucial for the planetary nitrogen cycle and biosphere, but requires substantial cellular energy resources. Here, we solved how energy-limited anaerobes regulate on-demand N2-fixation by sequestering their nitrogenase through the PII-nitrogen regulatory proteins NifI1 and NifI2. The nitrogenase was directly isolated from a methanogenic archaeon, with NifI proteins tightly bound. The crystal structure of the inhibited form, refined to 2.3-[A] resolution, reveals a supercomplex in which three NifI1,2 units made of a NifI1,2 heterohexamer captured three nitrogenases via tentacular T-loops. Additional structural information confirmed that NifI1,2 sits at the nitrogenase reductase-binding site, preventing N2-reduction. The presence of MgATP and 2-oxoglutarate releases NifI1,2 from the nitrogenase core via a conformational switch of the T-loops, provoking a steric repulsion and loss of contacts. The overall molecular depiction corroborates previous genetic, biochemical, and biophysical experiments, proposing that NifI1,2 disrupts the dynamic nitrogenase-reductase association, thereby interfering with electron delivery for N2-fixation and preventing ATP consumption. While ligand-binding mode and the T-loop conformational switch are expected to be conserved among NifI1,2-utilisers, the association mode with the nitrogenase comes in different flavours as a few substitutions in NifI2 break NifI1,2 intramolecular dimerisation in Methanosarcinales species, readjusting the supercomplex without altering the inhibition mechanism. With the NifI1,2 allosteric control dependent on the alarmone 2-oxoglutarate, anaerobes can effectively balance nitrogen-acquisition versus energy-expenditure, a regulatory switch that might be primitive and has been progressively lost in non-energy-limited aerobes, but could inspire biotechnological engineering to optimise ammonia bioproduction.

biochemistry↗

bioRxiv2025

Dynamic protrusions mediate unique crawling motility in Asgard Archaea (Promethearchaeota)

Crawling motility is a hallmark of eukaryotic cells and requires a dynamic actin cytoskeleton, regulated adhesion, and spatially organized signalling pathways1-3. Asgard archaea (phylum Promethearchaeota) which are considered the closest known prokaryotic relatives of eukaryotes potentially encode these functions within their large set of eukaryotic signature proteins4-9. The few cultivated members show a complex cell morphology, consisting of a central cell body from which several protrusions extend, filled with an actin-based cytoskeleton10,11. Here, live cell microscopy of two organisms of the Loki- and Hodarchaea lineages10,12 showed that they dynamically and drastically change their cell shape on a minute time scale and grow and retract their extensive protrusions with a speed of 1.5 to 5.3 {micro}m/min, respectively. After adhering to a glass surface, cells employ their protrusions to undergo active crawling motion. In the presence of selected actin inhibitors however, the observed dynamics were arrested, suggesting a central role of actin in these processes. The observed cellular plasticity and motility are unique features among prokaryotes and might have been crucial for the emergence of the first eukaryotic cells that are thought to have formed through the association of a member of the Promethearchaeota and an alphaproteobacterium, the ancestor of mitochondria.

microbiology↗

bioRxiv2025

Molecular basis of N2 fixation in a hyperthermophilic archaeon

Exploring the natural diversity of phylogenetically distant nitrogenases is crucial for gaining new insights into the mechanism of atmospheric N2 fixation and unlocking biotechnological developments in sustainable ammonia production. Here, we investigated the N2-fixing system of Methanocaldococcus infernus, a deep-sea hyperthermophilic archaeon growing diazotrophically at 92 {degrees}C. This natively isolated nitrogenase has a melting temperature close to the water boiling point, with an extrapolated specific activity superior to mesophilic homologues. The crystal structures obtained at near-atomic resolution present the most simplified known nitrogenase, harbouring strategic hot spots for thermostability. It combines the structural traits of all three known nitrogenase isoforms, reinforcing the postulate that the archaeal enzyme predates modern versions. In contrast to structural homologues, the electron-transferring metallocofactor "P-cluster" is trapped in a rare state awaiting electron delivery, providing a detailed picture of the physiological state. The active site, harbouring the FeMo-cofactor catalyst, exhibits a mixture of the resting and "turnover" states, previously described solely in the bacterial vanadium and iron-only nitrogenases. Therefore, these results unify a mechanistic principle of all nitrogenases and highlight the advantages of the hyperthermostable nature of the archaeal enzyme, opening new avenues for further understanding of how nature splits the N2 triple bond.

biochemistry↗

bioRxiv2022

Transcriptomics sheds light on N2-fixation strategies employed by a thermophilic member of the Methanococcales

Some marine thermophilic methanogens are able to perform energy-consuming nitrogen fixation despite deriving only little energy from hydrogenotrophic methanogenesis. We studied this process in Methanothermococcus thermolithotrophicus DSM 2095, a methanogenic archaeon of the order Methanococcales, that contributes to the nitrogen pool in some marine environments. We successfully grew this archaeon under diazotrophic conditions in both batch and fermenter cultures, reaching the highest cell density reported so far. Diazotrophic growth depended strictly on molybdenum and, in contrast to other diazotrophs, was not inhibited by tungstate or vanadate. This suggests an elaborate control of metal uptake and a specific metal recognition system for the insertion into the nitrogenase cofactor. Differential transcriptomics of M. thermolithotrophicus grown under diazotrophic conditions with ammonium-fed cultures as controls revealed upregulation of the nitrogenase machinery including chaperones, regulators, and molybdate-importers, as well as simultaneous upregulation of an ammonium-transporter and a putative pathway for nitrate/nitrite utilization. The organism thus employs multiple synergistic strategies for uptake of nitrogen nutrients during the early exponential growth phase without altering transcription levels for genes involved in methanogenesis. As a counterpart, genes coding for transcription and translation processes were downregulated, highlighting the maintenance of an intricate metabolic balance to deal with energy constraints and nutrient limitations imposed by diazotrophy. This switch in the metabolic balance included unexpected processes, such as upregulation of the CRISPR-Cas system, probably caused by drastic changes in transcription levels of putative mobile and virus-like elements. ImportanceThe thermophilic anaerobic archaeon, M. thermolithotrophicus, is a particularly suitable model organism to study the coupling of methanogenesis to diazotrophy. Likewise, its capability to simultaneously reduce N2/CO2 into NH3/CH4 with H2 makes it a viable target for biofuel production. We optimized M. thermolithotrophicus cultivation, resulting in considerably higher cell yields and enabling the successful establishment of N2-fixing bioreactors. Improved understanding of the N2-fixation process would provide novel insights into metabolic adaptations that allow this energy-limited extremophile to thrive under diazotrophy, for instance by investigating its physiology and uncharacterized nitrogenase. We demonstrate that diazotrophic growth of M. thermolithotrophicus is exclusively dependent on molybdenum, and complementary transcriptomics corroborated the expression of the molybdenum nitrogenase system. Further analyses of differentially expressed genes during diazotrophy across three cultivation time points revealed insights into the response to nitrogen limitation and the coordination of core metabolic processes.

microbiology↗