Biology subjects

Pfeiffer, F.

Publications and source records attributed to Pfeiffer, F..

13 recordsLinked to original sources

bioRxiv2026

Characterization of aliA and aliB deletion mutants reveals a dominant role of AliA in Haloferax volcanii lipoprotein lipidation

Protein lipidation is a widespread strategy for anchoring proteins to cellular membranes across all domains of life, yet the mechanisms underlying this process in archaea remain poorly understood. Recently, the first archaeal enzymes involved in lipobox-containing protein (lipoprotein) biogenesis, AliA and AliB, were identified and characterized in the model archaeon Haloferax volcanii. Although these paralogs share significant sequence similarity, distinct deletion phenotypes suggest differences in their substrate specificity and function. Here, we employed large-scale Triton X-114 fractionation followed by quantitative proteomics and lipid-specific mass spectrometry to systematically analyze AliA- and AliB-dependent lipoprotein lipidation. Deletion of aliA affected substantially more lipoproteins in Hfx. volcanii than deletion of aliB, markedly diminishing their TX-114 enrichment--indicating reduced hydrophobicity--and abolishing thioether-linked archaeol modification. This establishes AliA as the primary enzyme responsible for archaeal lipoprotein lipidation. In contrast, deletion of aliB affected only a small subset of lipoproteins and did not significantly reduce thioether-linked archaeol levels. In addition to defining distinct and non-redundant roles for AliA and AliB, this study provides the first large-scale experimental validation of predicted archaeal lipoproteins and identifies candidate components of the archaeal lipoprotein biogenesis pathway, substantially advancing mechanistic understanding and enabling improved lipoprotein prediction in this previously underexplored field.

molecular biology↗

bioRxiv2025

Oligodendrocyte precursor cells establish regulatory contacts with the soma of active neurons

Oligodendrocyte precursor cells (OPCs) generate myelinating oligodendrocytes and interact with synapses to regulate neuronal networks. Neuronal activity induces proliferation or differentiation of OPCs, but it is unknown whether OPCs in turn affect neuronal activity. Here, we show that OPCs establish close contacts with the somata of active neurons. We found that neurons contacted by OPCs and their processes display reduced calcium signals, indicating that they regulate their activity.

neuroscience↗

bioRxiv2024

Provirus deletion from Haloferax volcanii affects motility, stress resistance and CRISPR RNA expression

Haloferax volcanii harbours four putative proviruses: Halfvol1, Halfvol2, Halfvol3 and Halfvol4. In this study we successfully deleted all four provirus genomes, demonstrating, that they are not essential. Transcriptome comparison between this strain ({Delta}Halfvol1-4) and a wild type strain reveals an increase in archaella and chemotaxis gene expression, resulting in higher swarming motility in {Delta}Halfvol1-4. Furthermore, {Delta}Halfvol1-4 cells show an elongated cell shape and a higher resistance to H2O2 stress compared to the wild type. RNA-seq also revealed down-regulation of CRISPR arrays in the provirus-free strain. Circularised genomes of Halfvol1, Halfvol2 and Halfvol3 were found in the culture supernatant. This confirms excision of the proviruses from the chromosome, which seems to happen more efficiently at low temperature (30{degrees}C). Electron microscopy revealed potential viral particles in the supernatant, and mass spectrometry analysis confirmed the presence of structural viral proteins of Halfvol1 and Halfvol3 in the isolated virus sample. These observations suggest that these proviruses are active and cause a chronic infection in Hfx. volcanii.

molecular biology↗

bioRxiv2024

Beyond bacterial paradigms: uncovering the functional significance and first biogenesis machinery of archaeal lipoproteins

Lipoproteins are major constituents of prokaryotic cell surfaces. In bacteria, lipoprotein attachment to membrane lipids is catalyzed by prolipoprotein diacylglyceryl transferase (Lgt). However, no Lgt homologs have been identified in archaea, suggesting the unique archaeal membrane lipids require distinct enzymes for lipoprotein lipidation. Here, we performed in silico predictions for all major archaeal lineages and revealed a high prevalence of lipoproteins across the domain Archaea. Using comparative genomics, we identified the first set of candidates for archaeal lipoprotein biogenesis components (Ali). Genetic and biochemical characterization confirmed two paralogous genes, aliA and aliB, are important for lipoprotein lipidation in the archaeon Haloferax volcanii. Disruption of AliA- and AliB-mediated lipoprotein lipidation results in severe growth defects, decreased motility, and cell-shape alterations, underscoring the importance of lipoproteins in archaeal cell physiology. AliA and AliB also exhibit different enzymatic activities, including potential substrate selectivity, uncovering a new layer of regulation for prokaryotic lipoprotein lipidation.

microbiology↗

bioRxiv2024

Global distribution and diversity of haloarchaeal pL6-family plasmids

Australian isolates of Haloquadratum walsbyi, a square-shaped haloarchaeon, often harbor small cryptic plasmids of the pL6-family, approximately 6 kb in size. These plasmids exhibit a highly conserved gene arrangement and encode a replicase similar to those of betapleolipoviruses. To assess their global distribution and recover more examples for analysis, fifteen additional plasmids were reconstructed from the metagenomes of seven hypersaline sites across four countries: Argentina, Australia, Puerto Rico, and Spain. Including the five previously described plasmids, the average plasmid size is 6,002 bp, with an average G+C content of 52.5%. The tetramers GGCC and CTAG are either absent or significantly under-represented, except in the two plasmids with the highest %G+C. All plasmids share a similar arrange-ment of genes organized as outwardly facing replication and ATPase modules, but variations were observed in some core genes, such as F2, and some plasmids had acquired accessory genes. Two plasmids, pCOLO-c1 and pISLA-c6 shared 92.7% nt identity despite originating from Argentina and Spain, respectively. Numerous metagenomic CRISPR spacers matched sequences in the fifteen reconstructed plasmids, indicating frequent invasion of haloarchaea. Spacers could be assigned to haloarchaeal genera by mapping their associated direct repeats (DR), with half of these matching to Haloquadratum. Finally, strand-specific metatranscriptome (RNA-seq) data could be used to demonstrate the active transcription of two pL6-family plasmids, including antisense transcripts.

microbiology↗

bioRxiv2023

Axonopathy and altered synaptic development in early hippocampal epileptogenesis of Dravet syndrome

Dravet syndrome caused by SCN1A variants is a severe developmental epileptic encephalopathy (DEE) characterized by pharmaco-resistant epileptic seizures and progressive neurodevelopmental decline with cognitive impairment and autism-spectrum-traits. Numerous preceding studies indicate that the initial pathophysiology due to impaired NaV1.1 function mainly derives from reduced interneuron firing leading to a network hyperexcitability (Bender et al. 2012). However, little is known how epileptogenesis and generally disease pathogenesis progress from the inborn molecular defect to infantile seizure onset. We address this question in a Dravet mouse model by comprehensive single-cell RNA sequencing and selected downstream analysis via single-cell electrophysiology, histology, live cell imaging and electron microscopy. Our data reveal a continuum of early primary (preseizure) and secondary (post-seizure onset) transcriptomic changes in various cell populations in the hippocampus. Focusing on cornu ammonis, we find a number of transcriptional pathways that are dysregulated including synaptic transmembrane adhesion molecules of the neurexin superfamily and voltage-gated ion channels. Further investigations support an ultrastructural and functional axonopathy and synaptopathy of parvalbumin interneurons. These processes precede somatic firing impairment and seizures suggesting they underlie fundamental early-phase disease mechanisms. Taken together we provide a cellularly resolved transcriptomic resource of early disease phases of Dravet syndrome and demonstrate epileptogenesis beyond NaV1.1 loss-of-function during an early developmental time window of CNS maturation. Altogether these data establish proof-of principle that the concept of epileptogenesis, originally devised for acquired forms of epilepsy, similarly applies to genetic epilepsies and DEEs.

neuroscience↗

bioRxiv2023

Identification and characterization of structural and regulatory cell-shape determinants in Haloferax volcanii

Archaea play indispensable roles in global biogeochemical cycles, yet many critical cellular processes, including cell-shape determination, are poorly understood. Haloferax volcanii, a model haloarchaeon, forms rods and disks, depending on growth conditions. Here, we used a combination of iterative proteomics, genetics, and live-cell imaging to identify distinct mutants that only form rods or disks. We compared the proteomes of the mutants with wild-type cells across growth phases, thereby distinguishing between protein abundance changes specific to cell shape and those related to growth phases. The corresponding results indicated a diverse set of proteins, including transporters, transducers, signaling components, and transcriptional regulators, as important for cell-shape determination. We also identified structural proteins, including a previously unknown cytoskeletal element, the Hfx. volcanii actin homolog volactin, which plays a role in disk-shape morphogenesis. In summary, we gleaned important insights into archaeal cell-shape determination, with possible implications for understanding the evolution of cell morphology regulation across domains.

microbiology↗

bioRxiv2021

Open issues for protein function assignment in Haloferax volcanii and other halophilic archaea

BackgroundAnnotation ambiguities and annotation errors are a general challenge in genomics. While a reliable protein function assignment can be obtained by experimental characterization, this is expensive and time-consuming, and the number of such Gold Standard Proteins (GSP) with experimental support remains very low compared to proteins annotated by sequence homology, usually through automated pipelines. Even a GSP may give a misleading assignment when used as a reference: the homolog may be close enough to support isofunctionality, but the substrate of the GSP is absent from the species being annotated. In such cases the enzymes cannot be isofunctional. Here, we examine a variety of such issues in halophilic archaea (class Halobacteria), with a strong focus on the model haloarchaeon Haloferax volcanii. ResultsAnnotated proteins of Hfx. volcanii were identified for which public databases tend to assign a function that is probably incorrect. In some cases, an alternative, probably correct, function can be predicted or inferred from the available evidence but this has not been adopted by public databases because experimental validation is lacking. In other cases, a probably invalid specific function is predicted by homology, and while there is evidence that this assigned function is unlikely, the true function remains elusive. We list 50 of those cases, each with detailed background information so that a conclusion about the most likely biological function can be drawn. For reasons of brevity and comprehension, only key aspects are listed in the main text, with detailed information being provided in a corresponding section of the Supplementary Material. ConclusionsCompiling, describing and summarizing these open annotation issues and functional predictions will benefit the scientific community in the general effort to improve the evaluation of protein function assignments and more thoroughly detail them. By highlighting the gaps and likely annotation errors currently in the databases, we hope this study will provide a framework for experimentalists to systematically confirm (or disprove) our function predictions or to uncover yet unexpected functions.

bioinformatics↗

bioRxiv2021

Glycoproteomics of Haloferax volcanii reveals an extensive glycoproteome and concurrence of different N-glycosylation pathways

Glycosylation is one of the most complex post-translational protein modifications. Its importance has been established not only for eukaryotes but also for a variety of prokaryotic cellular processes, such as biofilm formation, motility and mating. However, comprehensive glycoproteomic analyses are largely missing in prokaryotes. Here we extend the phenotypic characterisation of N-glycosylation pathway mutants in Haloferax volcanii and provide a detailed glycoproteome for this model archaeon through the mass spectrometric analysis of intact glycopeptides. Using in-depth glycoproteomic datasets generated for the wild-type and mutant strains as well as a reanalysis of datasets within the Archaeal Proteome Project, we identify the largest archaeal glycoproteome described so far. We further show that different N-glycosylation pathways can modify the same glycosites under the same culture conditions. The extent and complexity of the Hfx. volcanii N-glycoproteome revealed here provides new insights into the roles of N-glycosylation in archaeal cell biology.

biochemistry↗

bioRxiv2021

Microglial Neuropilin-1 trans-regulates oligodendrocyte expansion during development and remyelination

NG2 glia or oligodendrocyte precursor cells (OPCs) are distributed throughout the gray and white matter and generate myelinating cells. OPCs in white matter proliferate more than those in gray matter in response to platelet-derived growth factor AA (PDGF AA), despite similar levels of its alpha receptor (PDGFR) on their surface. Here we show that the type 1 integral membrane protein Neuropilin-1 (Nrp1) is expressed not on OPCs but on amoeboid and activated microglia in white but not gray matter in an age- and activity-dependent manner. Microglia-specific deletion of Nrp1 compromised developmental OPC proliferation in white matter as well as OPC expansion and subsequent myelin repair after acute demyelination. Exogenous Nrp1 increased PDGF AA-induced OPC proliferation and PDGFR phosphorylation on dissociated OPCs, most prominently in the presence of suboptimum concentrations of PDGF AA. These findings uncover a novel mechanism of regulating oligodendrocyte lineage cell density that involves trans-activation of PDGFR on OPCs via Nrp1 expressed by adjacent microglia.

neuroscience↗

bioRxiv2020

Cellular and genomic properties of Haloferax gibbonsii LR2-5, the host of euryarchaeal virus HFTV1

Hypersaline environments are the source of many viruses infecting different species of halophilic euryarchaea. Information on infection mechanisms of archaeal viruses is scarce, due to the lack of genetically accessible virus-host models. Recently a new archaeal siphovirus, Haloferax tailed virus 1 (HFTV1), was isolated together with its host belonging to the genus Haloferax, but it is not infectious on the widely used model euryarcheon Hfx. volcanii. To gain more insight into the biology of HFTV1 host strain LR2-5, we studied characteristics that might play a role in its virus susceptibility: growth-dependent motility, surface layer, filamentous surface structures and cell shape. Its genome sequence showed that LR2-5 is a new strain of Hfx. gibbonsii. LR2-5 lacks obvious viral defense systems, such as CRISPR-Cas, and the composition of its cell surface is different from Hfx. volcanii, which might explain the different viral host range. This work provides first deep insights into the relationship between the host of halovirus HFTV1 and other members of the genus Haloferax. Given the close relationship to the genetically accessible Hfx. volcanii, LR2-5 has high potential as a new model for virus-host studies in euryarchaea.

microbiology↗

bioRxiv2019

LIPID ANCHORING OF ARCHAEOSORTASE SUBSTRATES AND MID-CELL GROWTH IN HALOARCHAEA

The archaeal cytoplasmic membrane provides an anchor for many surface proteins. Recently, a novel membrane anchoring mechanism involving a peptidase, archaeosortase A (ArtA) and C-terminal lipid attachment of surface proteins was identified in the model archaeon Haloferax volcanii. ArtA is required for optimal cell growth and morphogenesis, and the S-layer glycoprotein (SLG), the sole component of the H. volcanii cell wall, is one of the targets for this anchoring mechanism. However, how exactly ArtA function and regulation control cell growth and mor-phogenesis is still elusive. Here, we report that archaeal homologs to the bacterial phos-phatidylserine synthase (PssA) and phosphatidylserine decarboxylase (PssD) are involved in ArtA-dependent protein maturation. H. volcanii strains lacking either HvPssA or HvPssD exhibited motility, growth and morphological phenotypes similar to those of {triangleup}artA. Moreover, we showed the loss of covalent lipid attachment to SLG in the {triangleup}hvpssA mutant and that proteolytic cleavage of the ArtA substrate HVO_0405 was blocked in the {triangleup}hvpssA and {triangleup}hvpssD strains. Strikingly, ArtA, HvPssA, and HvPssD GFP-fusions co-localized to the mid position of H. volcanii cells, strongly supporting that they are involved in the same pathway. Finally, we have shown that the SLG is also recruited to the mid cell prior to being secreted and lipid-anchored at the cell outer surface. Collectively, our data suggest haloarchaea use the mid cell as the main surface processing hotspot for cell elongation, division and shape determination.

cell biology↗

bioRxiv2019

Unbiased Map of Transcription Termination Sites in Haloferax volcanii reveals manifold termination patterns

Archaeal genomes are densely packed; thus, correct transcription termination is an important factor for orchestrated gene expression. A systematic analysis of RNA 3 termini, to identify transcription termination sites (TTS) using RNAseq data has hitherto only been performed in two archaea. In this study, only part of the genome had been investigated. Here, we developed a novel algorithm that allows an unbiased, genome-wide identification of RNA 3 termini independent of annotation. In an RNA fraction enriched for primary transcripts by terminator exonuclease (TEX) treatment we identified 1,543 RNA 3 termini. A strong sequence signature consistent with known termination events at intergenic loci indicates a clear enrichment for native TTS among them. Using these data we determined distinct putative termination motifs for intergenic (a T stretch) and coding regions (AGATC). In vivo reporter gene tests of selected TTS confirmed termination at these sites, which exemplify the different motifs. For several genes, more than one termination site was detected, resulting in transcripts with different lengths of the 3 untranslated region.

molecular biology↗