Biology subjects

Gieselmann, V.

Publications and source records attributed to Gieselmann, V..

4 recordsLinked to original sources

bioRxiv2026

ER-Lysosome Cholesterol Exchange Regulates Lysosomal Motility Through mTOR-Dependent LAMTOR1 Phosphorylation

The subcellular distribution of lysosomes, the main degradative organelles of mammalian cells, responds to metabolic cues in a highly dynamic way. While lysosomal positioning due to amino acid levels is well-characterized, cholesterol-dependent regulation of lysosomal motility is incompletely understood. We explored impaired lysosomal cholesterol export using a mass spectrometry-based multi-OMICs approach, identifying widespread reallocation of resources and signaling pathway modulation. We identified increased phosphorylation at LAMTOR1 serine 56 in response to cholesterol level perturbations. We demonstrate that this phosphorylation site is sufficient to disrupt Rag GTPases/SLC38A9 binding to the Ragulator complex, inhibiting canonical mTORC1 and facilitating binding of BORC, therefore promoting lysosomal retrograde movement. LAMTOR1 S56 phosphorylation responds exclusively to depletion of lysosomal limiting membrane cholesterol, is facilitated by mTOR, and presents a negative feedback loop for amino acid independent displacement of Ragulator bound Rag GTPases, limiting canonical mTORC1 activity. Mass spectrometry data are available via ProteomeXchange with identifier PXD073489. HighlightsO_LIPerturbation of lysosomal cholesterol homeostasis results in adaptation of cellular protein and lipid biosynthesis C_LIO_LILAMTOR1 is phosphorylated at serine 56 via mTORC1 C_LIO_LILAMTOR1 S56 phosphorylation is lysosomal membrane cholesterol dependent C_LIO_LILAMTOR1 S56 phosphorylation disrupts binding of Rag GTPases to the Ragulator complex C_LIO_LILAMTOR1 S56 phosphorylation promotes binding of Ragulator to BORC, facilitating lysosomal retrograde transport C_LI

molecular biology↗

bioRxiv2025

Absolute Quantification of Lysosomal Proteins by Multiple Reaction Monitoring Mass Spectrometry and QconCAT Protein Standards

ABSTRACTLysosomes are membrane-enclosed organelles that play a crucial role in the degradation of intra- and extracellular substrates and the regulation of metabolic signaling. These functions are carried out by a variety of proteins, of which > 150 are currently known to be located in the lysosomal lumen or to be embedded in its membrane. These proteins are typically low abundant, necessitating organelle enrichment experiments to enable their investigation by unbiased mass spectrometry-based proteomics analyses. Enrichment strategies have been applied in a plethora of studies to gain a deeper understanding of lysosomal composition and relative changes of lysosomal proteome abundance in a variety of pathological conditions. Such experiments are restricted, however, to selected cell lines and tissues and do not allow a direct analysis of the lysosomal proteome from whole cell or tissue lysates. Furthermore, they do not provide absolute quantities. We developed a multiple reaction monitoring mass spectrometry-based assay for the highly sensitive and reproducible absolute quantification of 143 mouse lysosomal proteins from any type of sample following the QconCAT strategy. We applied our approach to the investigation of mouse embryonic fibroblast whole cell lysates and lysosome-enriched fractions, providing absolute copy numbers per cell/lysosome for lysosomal hydrolases and membrane proteins. These data reveal a dynamic range of more than three orders of magnitude in protein expression and strong differences in the subcellular distribution of individual lysosomal proteins. Furthermore, we applied our strategy to the investigation of four primary cell types (macrophages, lung fibroblasts, osteoblasts, and osteoclasts), demonstrating pathway-specific heterogeneity of individual lysosomal protein classes and indicating protein-specific post-transcriptional regulation of expression levels.

molecular biology↗

bioRxiv2023

Proteomic Investigation of Neural Stem Cell to Oligodendrocyte Precursor Cell Differentiation Reveals Phosphorylation-Dependent Dclk1 Processing

Oligodendrocytes are generated via a two-step mechanism from pluripotent neural stem cells (NSCs): after differentiation of NSCs to oligodendrocyte precursor/NG2 cells (OPCs), they further develop into mature oligodendrocytes. The first step of this differentiation process is only incompletely understood. In this study, we utilized the neurosphere assay to investigate NSC to OPC differentiation in a time course-dependent manner by mass spectrometry-based (phospho-) proteomics. We identify double cortin like kinase 1 (Dclk1) as one of the most prominently regulated proteins in both datasets, and show that it undergoes a gradual transition between its short/long isoform during NSC to OPC differentiation. This is regulated by phosphorylation of its SP-rich region, resulting in inhibition of proteolytic Dclk1 long cleavage, and therefore Dclk1 short generation. Through interactome analyses of different Dclk1 isoforms by proximity biotinylation, we characterize their individual putative interaction partners and substrates.

cell biology↗

bioRxiv2022

Cross-linking of the Endolysosomal System Reveals Flotillin Structures and Putative Cargo

Lysosomes are well-established as the main cellular organelles for the degradation of macromolecules and emerging as regulatory centers of metabolism. They are of crucial importance for cellular homeostasis, which is exemplified by a plethora of disorders related to alterations in lysosomal function. In this context, protein complexes play a decisive role, regulating not only metabolic lysosomal processes, but also lysosome biogenesis, transport, and interaction with other organelles. Using cross-linking mass spectrometry, we analyzed lysosomes and early endosomes. Based on the identification of 5,376 cross-links, we investigated protein-protein interactions and structures of lysosome- and endosome-related proteins. In particular, we present evidence for a tetrameric assembly of the lysosomal hydrolase PPT1 and heterodimeric/- multimeric structures of FLOT1/FLOT2 at lysosomes and early endosomes. For FLOT1-/FLOT2- positive early endosomes, we identified >300 proteins presenting putative cargo, and confirm the latrophilin family of adhesion G protein-coupled receptors as substrates for flotillin-dependent endocytosis.

biochemistry↗