Biology subjects

Westermann, S.

Publications and source records attributed to Westermann, S..

7 recordsLinked to original sources

bioRxiv2026

Local albumin excess exacerbates Candida albicans-induced inflammasome activation underlying the immunopathology of vulvovaginal candidiasis.

Vulvovaginal candidiasis (VVC) is a mucosal yeast infection where symptoms are driven by inflammatory responses. The onset of VVC is instigated by the yeast Candida albicans, but the underlying causes of disease-driving hyperinflammation remains incompletely resolved. We found that vaginal albumin concentrations are higher in women with recurrent VVC and during VVC in mice. These albumin levels correlated with inflammatory cytokines in vaginal lavages. While the abundance of this serum protein in the vagina can represent a hallmark of inflammation-induced vascular permeability, we reveal molecular mechanisms by which albumin also drives inflammation. It increased NLRP3 inflammasome activation in human macrophages elicited by C. albicans. Albumin induced fungal adaptations that increased resistance to macrophage-mediated clearance. Further it increased the expression of fungal secreted aspartic protease 1, which we identified as the effector driving inflammasome activation. Moreover, neutrophils show impaired effectivity in clearing C. albicans in presence of albumin. Collectively, vaginal albumin may not only be a consequence of inflammation of the vaginal mucosa, but also can drive hyperinflammatory responses that underlie immunopathology in VVC. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=187 SRC="FIGDIR/small/700771v1_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@f13fd5org.highwire.dtl.DTLVardef@95e58aorg.highwire.dtl.DTLVardef@11104dforg.highwire.dtl.DTLVardef@56e9be_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

Phage-Assisted Evolution of Allosteric Protein Switches

Allostery, the transmission of locally induced conformational changes to distant functional sites, is a key mechanism for protein regulation1. Artificial allosteric effectors enable remote manipulation of cell function2,3; their engineering, however, is hampered by our limited understanding of allosteric residue networks. Here, we introduce a phage-assisted evolution4 platform for in vivo optimization of allosteric proteins. It applies opposing selection pressures to enhance activity and switchability of phage-encoded effectors and leverages retron-based recombineering5 to broadly explore fitness landscapes, introducing point mutations, insertions, and deletions. Applying this framework to the transcription factor AraC yielded near-binary optogenetic switches, with light-controlled activity spanning [~]1,000-fold dynamic range. Long-read sequencing across selection cycles enabled high-resolution tracking of evolving variant pools, revealing adaptive trajectories and context-dependent residue interactions. Mechanistically, we found that linker mutations promoting -helix extension at the sensor-effector junction enhance conformational coupling between LOV2 and AraC. These variants emerged consistently across independently evolved pools, underscoring their functional relevance. Together, we developed a framework for the directed evolution of programmable allosteric switches in vivo. By coupling dynamic selection with deep mutational scanning and temporal sequencing, it enables both functional optimization and mechanistic insight into allosteric networks.

synthetic biology↗

bioRxiv2024

The Spc105-Kre28 complex promotes mitotic error correction by outer kinetochore recruitment of the Ipl1/Aurora B kinase

Kinetochores link chromosomes to dynamic microtubules of the mitotic spindle. To ensure equal chromosome segregation, sister chromatids must achieve biorientation. The conserved kinase Aurora B phosphorylates outer kinetochore proteins on attachments lacking tension, allowing re-establishment of new connections until biorientation is achieved. Aurora B localizes to the centromere as part of the chromosomal passenger complex (CPC), but the underlying recruitment pathways can be eliminated without disrupting biorientation. It therefore remains unclear how the kinase operates during error correction. Here, we identify the conserved Spc105/Kre28 complex as an outer kinetochore receptor of the Aurora kinase Ipl1 and its activator Sli15 in Saccharomyces cerevisiae. We show that mutations in the helix bundle domain of Spc105/Kre28 impair mitotic error correction, resembling the effects of ipl1 or sli15 mutants. The defects can be suppressed by artificial recruitment of Ipl1. In biochemical experiments Ipl1/Sli15 directly associates with Spc105/Kre28, and a conserved segment in the Sli15 central domain is crucially involved in the binding mechanism. These results have important implications for the mechanism of tension-dependent error correction during chromosome biorientation.

cell biology↗

bioRxiv2023

Ipl1-controlled attachment maturation regulates Mps1 association with its kinetochore receptor

Faithful chromosome segregation requires that sister chromatids establish bi-oriented kinetochore-microtubule attachments. The spindle assembly checkpoint (SAC) prevents premature anaphase onset with incomplete attachments. However, how microtubule attachment and checkpoint signaling are coordinated remains unclear. The conserved kinase Mps1 initiates SAC signaling by localizing transiently to kinetochores in prometaphase and is released upon bi-orientation. Using biochemistry, structure predictions, and cellular assays, we shed light on this dynamic behaviour in Saccharomyces cerevisiae. A conserved N-terminal segment of Mps1 binds the neck region of Ndc80:Nuf2, the main microtubule receptor of kinetochores. Mutational disruption of this interface, located at the backside of the paired CH-domains and opposite the microtubule-binding site, prevents Mps1 localization, eliminates SAC signalling, and impairs growth. The same interface of Ndc80:Nuf2 binds the microtubule-associated Dam1 complex. We demonstrate that the error correction kinase Ipl1/Aurora B controls the competition between Dam1 and Mps1 for the same binding site. Thus, binding of the Dam1 complex to Ndc80:Nuf2 may release Mps1 from the kinetochore to allow anaphase onset.

cell biology↗

bioRxiv2022

Systematic analysis of microtubule plus-end networks defines EB-cargo complexes critical for mitosis in budding yeast

Microtubules are ubiquitous cytoskeletal polymers with essential functions in chromosome segregation, intracellular transport and cellular morphogenesis. End-binding proteins (EBs) form the nodes of intricate microtubule plus-end interaction networks. Which EB binding partners are most critical for cell division, and how cells manage to organize a microtubule cytoskeleton in the absence of an EB protein, are open questions. Here we demonstrate that the budding yeast EB protein Bim1 executes its key mitotic functions as part of two cargo complexes-Bim1-Kar9 in the cytoplasm and Bim1-Cik1-Kar3 in the nucleus. Lack of Bim1-Kar9 during spindle orientation is compensated by accumulation of the CLIP-170 homolog Bik1 on the lattice of long cytoplasmic microtubules, which upregulates the Dynein-Dynactin nuclear migration pathway. In the nucleus a Bim1-Bik1-Cik1-Kar3 complex acts during initial metaphase spindle assembly and supports sister chromatid bi-orientation. Lack of Bim1 alters spindle association timing and the level of the microtubule crosslinkers Ase1/PRC1 and Slk19, which become essential for bi-orientation. Engineered plus-end targeting of Kinesin-14 Cik1-Kar3 efficiently restores major spindle-related bim1{tau}{iota} phenotypes. In addition to defining the key Bim1-cargo complexes our study also reveals compensatory mechanisms that allow cells to proliferate in the absence of Bim1.

cell biology↗

bioRxiv2021

Differentially accessible Cdc4 phospho-degrons regulate Ctf19CCAN kinetochore subunit stability in mitosis

Kinetochores are multi-subunit protein assemblies that link chromosomes to microtubules of the mitotic and meiotic spindle. How effective, yet strictly centromere-dependent kinetochore assembly is coupled to cell cycle progression is incompletely understood. Here, by combining comprehensive phosphorylation analysis of native Ctf19CCAN subunits with biochemical and functional assays in the model system budding yeast, we demonstrate that Cdk1 phosphorylation activates phospho-degrons on the essential subunit Ame1CENP-U which are recognized by the E3 ubiquitin ligase complex SCF-Cdc4. Gradual phosphorylation of degron motifs culminates in M-Phase and targets the protein for degradation. Binding of the Mtw1 complex shields the proximal phospho-degron, protecting kinetochore-bound Ame1 from the degradation machinery. Artificially increasing degron strength partially suppresses the temperature-sensitivity of a cdc4 mutant, while overexpression of Ame1-Okp1 is toxic to cells, demonstrating the physiological importance of this mechanism. We propose that phospho-regulated clearance of excess CCAN subunits protects against ectopic kinetochore assembly and contributes to mitotic checkpoint silencing. Our results suggest a novel strategy for how phospho-degrons can be used to regulate the assembly of multi-subunit complexes.

cell biology↗

bioRxiv2020

Selective REM-Sleep Suppression Increases Next-Day Negative Affect and Amygdala Responses to Social Exclusion

Healthy sleep, positive general affect, and the ability to regulate emotional experiences are fundamental for well-being. In contrast, various mental disorders are associated with altered rapid eye movement (REM) sleep, negative affect, and diminished emotion regulation abilities. However, the neural processes mediating the relationship between these different phenomena are still not fully understood. In the present study of 42 healthy volunteers, we investigated the effects of selective REM sleep suppression (REMS) on general affect, as well as on feelings of social exclusion, emotion regulation, and their neural underpinnings. Using functional magnetic resonance imaging we show that REMS increases amygdala responses to experimental social exclusion, as well as negative affect on the morning following sleep deprivation. There was no evidence that emotional responses to experimentally induced social exclusion or their regulation using cognitive reappraisal were impacted by diminished REM sleep. Our findings indicate that general affect and amygdala activity depend on REM sleep, while specific emotional experiences possibly rely on additional psychological processes and neural systems that are less readily influenced by REMS.

neuroscience↗