Biology subjects

Bohnert, M.

Publications and source records attributed to Bohnert, M..

7 recordsLinked to original sources

bioRxiv2025

Role of Pex31 in metabolic adaptation of the nucleus vacuole junction NVJ

The nucleus vacuole junction NVJ in yeast is a multifunctional contact site between the nuclear ER membrane and the vacuole with diverse roles in lipid metabolism, transfer and storage. Adaptation of NVJ functions to metabolic cues is mediated by a striking remodeling of the size and the proteome of the contact site, but the extent and the molecular determinants of this plasticity are not fully understood. Using microscopy-based screens, we monitored NVJ remodeling in response to glucose availability. We identified Pex31, Nsg1, Nsg2, Shr5, and Tcb1 as NVJ residents. Glucose starvation typically results in an expansion of the NVJ size and proteome. Pex31 shows an atypical behavior, being specifically enriched at the NVJ at high glucose conditions. Loss of Pex31 uncouples NVJ remodeling from glucose availability, resulting in recruitment of glucose starvation-specific residents and NVJ expansion at glucose replete conditions. Moreover, PEX31 deletion results in alterations of sterol ester storage and a remodeling of vacuolar membranes that phenocopy glucose starvation responses. We conclude that Pex31 has a role in metabolic adaptation of the NVJ. SUMMARY STATEMENTUsing microscopy-based screens in yeast, we identified Pex31, Nsg1, Nsg2, Shr5 and Tcb1 as residents of the nucleus vacuole junction NVJ. Pex31 has a role in NVJ adaptation to glucose availability.

cell biology↗

bioRxiv2025

The Myo2 adaptor Ldm1 and its receptor Ldo16 mediate actin-dependent lipid droplet motility

Organelle motility enables strategic cellular reorganizations. In yeast, this process depends on the actin cytoskeleton, type V myosin motor proteins, and organelle-specific myosin adaptor proteins. While the myosin adaptors for most organelles are known, the coupling of myosin to lipid droplets (LDs), the cellular lipid storage organelles, remained enigmatic. Using genome-wide screening, we identified Ldm1 (Lipid Droplet Motility 1/Yer085c) as a myosin adaptor. Ldm1 binds to the globular tail domain of the myosin Myo2 and to the LD surface protein Ldo16 to enable actin-dependent LD motility. Ldo16 has additional roles in LD contact sites to the vacuole and the ER, suggesting a coordination of LD motility and organelle tethering. Ldm1 has a second role in mitochondrial transport and elevated Ldm1 levels rescue defects of the mitochondrial Myo2-adaptors Mmr1/Ypt11. Our work identifies the molecular machinery for LD motility and contributes to a comprehensive understanding of acto-myosin-based cellular reorganization.

cell biology↗

bioRxiv2024

Pex3 promotes formation of peroxisome-peroxisome and peroxisome-lipid droplet contact sites

Peroxisomes are ubiquitous organelles that mediate central metabolic functions, such as fatty acid {beta}-oxidation, as well as diverse tissue- and organism-specific processes. Membrane contact sites, regions of close apposition with other organelles for direct communication, are central to several aspects of their life cycle. Pex3 is a conserved multifunctional peroxisomal transmembrane protein involved in the insertion of peroxisomal membrane proteins, in pexophagy, and in the formation of membrane contact sites. Here, we show that elevated Pex3 levels in Saccharomyces cerevisiae induce the formation of peroxisome clusters surrounded by lipid droplets, mediated by peroxisome-peroxisome and peroxisome-lipid droplet contact sites. This clustering occurs independently of Pex3 partners in other processes, Pex19, Inp1, and Atg36. The cytosolic domain of Pex3 binds peroxisomes, suggesting a direct role in homotypic contact site formation. Lipid droplet-peroxisome contact sites require the lipid droplet-localized triacylglycerol lipase Tgl4, which is enriched along with other lipases at this interface. Pex3 overexpression in Drosophila melanogaster similarly alters peroxisome and lipid droplet morphology and promotes contact site formation. Together, our results offer novel molecular insights into homotypic peroxisome contact sites and peroxisome-lipid droplet contact sites across species.

cell biology↗

bioRxiv2024

Coordination of cytochrome bc1 complex assembly at MICOS

The boundary and cristae domains of the mitochondrial inner membrane are connected by crista junctions. Most cristae membrane proteins are nuclear-encoded and inserted by the mitochondrial protein import machinery into the inner boundary membrane. Thus, they must overcome the diffusion barrier imposed by crista junctions to reach their final location. Here, we show that respiratory chain complexes and assembly intermediates are physically connected to the mitochondrial contact site and cristae organizing system (MICOS) that is essential for formation and stability of crista junctions. We identify the inner membrane protein Mar26 (Fmp10) as determinant in the biogenesis of the cytochrome bc1 complex (complex III). Mar26 couples a Rieske Fe/S protein-containing assembly intermediate to MICOS. Our data indicate that Mar26 maintains an assembly-competent Rip1 pool at crista junctions where complex III maturation likely occurs. MICOS facilitates efficient Rip1 assembly by recruitment of complex III assembly intermediates to crista junctions. We propose that MICOS, via interaction with assembly factors such as Mar26, directly contributes to the spatial and temporal coordination of respiratory chain biogenesis.

biochemistry↗

bioRxiv2023

A metabolically controlled contact site between lipid droplets and vacuoles

The lipid droplet (LD) organization proteins Ldo16 and Ldo45 affect multiple aspects of LD biology in yeast. They are linked to the LD biogenesis machinery seipin, and their loss causes defects in LD positioning, protein targeting, and breakdown. However, their molecular roles remained enigmatic. Here we report that Ldo16/45 form a tether-complex with Vac8 for creation of vacuole lipid droplet (vCLIP) contact sites, which can form in the absence of seipin. The phosphatidylinositol transfer protein Pdr16 is a further vCLIP-resident recruited by Ldo45. While only an LD-subpopulation is engaged in vCLIPs at glucose-replete conditions, nutrient stress results in vCLIP expansion, and vCLIP defects impair lipophagy upon prolonged starvation. In summary, Ldo16/45 are multifunctional proteins that orchestrate formation of a metabolically-regulated contact site. Our studies suggest an unexpected link between LD biogenesis and breakdown, and open the door to a deeper understanding of how lipid homeostasis is maintained during metabolic challenges.

cell biology↗

bioRxiv2023

Human dorsal root ganglia after plexus injury: either preservation or loss of the multicellular unit

ObjectivePlexus injury results in lifelong suffering of flaccid paralysis, sensory loss, and intractable pain. For this clinical problem, regenerative medicine concepts, such as cell replacement for restoring dorsal root ganglion (DRG) function, set high expectations. However, it is completely unclear which DRG cell types are affected by plexus injury. MethodsWe investigated the cellular composition of human DRG in a clinically characterized cohort of patients with plexus injury. Avulsed DRG of 13 patients were collected during reconstructive nerve surgery. Then, we analyzed the cellular composition of the DRG with a human-adapted objective deep learning-based analysis of large-scale microscopy images. ResultsSurprisingly, in about half of the patients, the injury-affected DRG no longer contained DRG cells. The complete entity of neurons, satellite glial cells, and microglia was lost and replaced by mesodermal/connective tissue. In the other half of patients, the cellular entity of the DRG was well preserved. We found no loss of neurons, no gliosis, and macrophages close to single sensory neuron/satellite glial cell entities. Patients with neuronal preservation had less pain than patients with neuronal loss. InterpretationThe findings classify plexus injury patients in two categories: type I (neuronal preservation) and type II (neuronal loss). We call for early, post-accidental interventions to protect the entire DRG and improved MRI diagnostics to detect neuronal loss. Regenerative medicine to restore DRG function will need at least two translational directions: reafferentation of existing DRG units for type I injuries; or replacement of the entire DRG structure for type II patients.

neuroscience↗

bioRxiv2021

A yeast lysosomal biogenesis map uncovers the cargo spectrum of lysosomal protein targeting pathways

The lysosome is the major catabolic organelle and a key metabolic signaling center of the cell. Mutations in lysosomal proteins can have catastrophic effects, causing neurodegeneration, cancer, and age-related diseases. The vacuole is the lysosomal analog of Saccharomyces cerevisiae that harbors many conserved proteins. Vacuolar proteins reach their destination via the endosomal vacuolar protein sorting (VPS) pathway, via the alkaline phosphatase (ALP or AP-3) pathway, and via the cytosol-to-vacuole transport (CVT) pathway. While these pathways have been extensively studied, a systematic understanding of the cargo spectrum of each pathway is completely lacking. Here we combine quantitative proteomics of purified vacuoles with mutant analyses to generate the lysosomal biogenesis map. This dataset harbors information on the cargo-receptor relationship of virtually all vacuolar proteins. We map binding motifs of Vps10 and the AP-3 complex and identify a novel cargo of the CVT pathway under nutrient-rich conditions. Our data uncover how organelle purification and quantitative proteomics can uncover fundamental insights into organelle biogenesis.

cell biology↗