Biology subjects

Morsomme, P.

Publications and source records attributed to Morsomme, P..

6 recordsLinked to original sources

bioRxiv2026

Cell-free membrane systems reveal electrostatic control of ion transport in TMEM165 and disease-associated CaCA2 variants

Ion transport across intracellular membranes is essential for cellular homeostasis, yet organellar transport mechanisms remain difficult to resolve in native cells. Here, we establish a cell-free membrane system to interrogate full-length intracellular transporters under defined chemical conditions. Using cell-free protein synthesis, human Golgi transporter TMEM165 and its yeast homolog GDT1 were synthesized in membranes and analyzed by fluorescence and electrochemical measurements. The platform controlled protein identity, ion composition, and transmembrane pH gradients. TMEM165 transport was regulated by pH gradients, consistent with proton-coupled transport shaped by the electrostatic environment of the transport pathway. Disruption of a conserved acidic residue decreased pH sensitivity, broadened ion permeability, and altered steady-state transport behavior, indicating impaired proton coupling and selectivity. These findings identify conserved acidic residues as key regulators of TMEM165 function. More broadly, this work establishes a strategy for reconstructing organellar membrane proteins, resolving disease mechanisms, and engineering transport function in defined synthetic systems.

biophysics↗

bioRxiv2026

A cleavable signal peptide controls the topology and Golgi targeting of the membrane protein TMEM165

TMEM165 is a Golgi-resident multi-pass membrane protein involved in divalent cation homeostasis and associated with congenital disorders of glycosylation, yet its N-terminal biogenesis has remained unresolved. Here, we demonstrate that TMEM165 contains a functional cleavable signal peptide required for correct Golgi targeting and membrane topology. Loss of this signal peptide causes protein mislocalization, and altered topology with N-terminal cytosolic exposure, whereas extended N-terminal deletion restores both Golgi localization and overall membrane topology, consistent with insertion mediated by the first transmembrane domain as commonly described for multi-pass membrane proteins. Importantly, this N-terminally truncated form remains responsive to manganese-induced degradation and partially restores glycosylation defects associated with TMEM165 deficiency, indicating that the extended N-terminal region is dispensable for core TMEM165 function. Together, these findings identify the signal peptide as a key determinant of TMEM165 biogenesis and suggest that its conservation may contribute not only to membrane targeting, but also to maintaining the proper luminal environment of the N-terminus during early biogenesis.

cell biology↗

bioRxiv2026

Proteomic Response of Thalassiosira pseudonana to Anoxia Reveals Alanine Fermentation Pathway and Reprogramming of Nitrogen Metabolism

O_LIDiatoms are key players in marine ecosystems and are frequently exposed to low-oxygen conditions in sediments and oxygen minimum zones. However, the metabolic strategies that enable their survival under anoxia remain poorly understood. C_LIO_LIUsing the model diatom Thalassiosira pseudonana, we investigated its response to dark anoxia. We first used proteomic approaches to identify differences between dark anoxia and dark oxic conditions combined with a phylogenetic analysis to decipher how the anoxic tolerance was acquired by this lineage. This approach revealed unexpected shunts involving amino acid pathways. We then correlated these findings with targeted metabolomic analysis on amino acids. C_LIO_LIOur results show that the diatom T. pseudonana undergoes a coordinated metabolic reprogramming under anoxia, centered on alanine production and tightly coupled to nitrogen metabolism. This work reveals how carbon and nitrogen fluxes are integrated to maintain cellular homeostasis in the absence of oxygen and provides a framework for understanding the resilience of diatoms in oxygen-depleted environments. C_LIO_LIWe identify three key features for anoxic adaptation in this lineage (i) alanine-centered metabolic reprogramming as a central component of acclimation to anoxia (ii) the involvement of an arginine-succinate shunt; and (iii) a critical contribution of lateral gene transfer (LGT) for anoxic tolerance. C_LI

plant biology↗

bioRxiv2025

A Unique LHCE Light-Harvesting protein Family is involved in Photosystem I and II Far-Red Absorption in Euglena gracilis

Photosynthetic organisms have evolved diverse strategies to adapt to fluctuating light conditions, balancing efficient light capture with photoprotection. In green algae and land plants, this involves specialized light-harvesting complexes (LHCs), non-photochemical quenching, and state transitions driven by dynamic remodeling of antenna proteins associated with Photosystems (PS) I and II. Euglena gracilis, a flagellate with a secondary green plastid, represents a distantly related lineage whose light-harvesting regulation remains poorly understood. Although spectral shifts under different light regimes have been observed, their molecular basis was unknown. Here, through integrated phylogenomic, proteomic, structural, and spectroscopic analyses, we identify a novel chlorophyll a far-red-absorbing antenna complex in E. gracilis, composed of a species-specific Lhce protein family. This antenna forms a pentameric complex under low light and transiently associates with PSII during far-red light exposure. It is structurally and functionally distinct from canonical LHCII{square} trimers and absent in Viridiplantae. Additionally, PSI in E. gracilis is surrounded by an expanded Lhce/LhcbM belt around a minimal core. These findings reveal a unique mechanism for regulating PS antenna size in E. gracilis, distinct from known models in plants and green algae, and highlight an alternative evolutionary strategy for light acclimation in organisms with secondary plastids. HighlightEuglena gracilis features a unique, lineage-specific LhcE antenna system that dynamically associates with PSII and expands PSI light harvesting, revealing an alternative strategy for light acclimation in secondary plastids.

plant biology↗

bioRxiv2024

Clathrin-independent endocytosis and retrograde transport in cancer cells promote cytotoxic CD8 T cell activation

Endophilin A3-mediated clathrin-independent endocytosis (EndoA3-mediated CIE) contributes to the internalization of immunoglobulin-like proteins, including key immune synapse components. Here, we identify ICAM1 as a novel EndoA3-dependent cargo, alongside ALCAM. We demonstrate that both proteins subsequently follow retromer-dependent retrograde transport to the trans-Golgi network (TGN) in cancer cells. From there, we propose that they undergo polarized redistribution to the plasma membrane, where they contribute to immune synapse formation between cancer cells and cytotoxic CD8 T cells. Disruption of EndoA3 or retromer components significantly affects the response of autologous cytotoxic CD8 T cells, as evidenced by reduced cytokine production and secretion, but increased lytic activity, while proliferation and later activation marker expression remain intact. This is accompanied by diminished ICAM1 density at the immune synapse, where we observe it arriving via polarized vesicular transport, indicating altered synapse organization. Indeed, cancer cells lacking EndoA3-mediated CIE or retromer form enlarged immune synapses that fail to sustain full T cell cytokine secretion, suggesting a compensatory attempt by T cells to overcome the defective synapse, while likely promoting more transient contacts that potentially favor serial killing. Together, these findings reveal that EndoA3-mediated CIE and retrograde transport act in concert in cancer cells to relocate immune synapse components via the Golgi, thereby fine-tuning the balance between cytotoxic T cell cytokine secretion and lytic activity. These insights contribute to a better understanding of the mechanisms governing immune synapse formation and organization, providing a necessary foundation for the long-term identification of new strategies to enhance T cell-mediated anti-tumor immunity. Significance StatementThis study uncovers a novel mechanism by which clathrin-independent endocytosis (CIE) and retrograde transport collaborate to regulate immune synapse dynamics in cancer cells. We identify ICAM1 as a new cargo of Endophilin A3-mediated CIE, highlighting its role in the polarized redistribution of immune synapse components critical for cytotoxic CD8 T cell activation. By linking a specific CIE mechanism and retrograde transport to immune synapse function, our findings provide new insights into cancer-immunity interactions and suggest potential therapeutic strategies to enhance immune responses by targeting protein trafficking pathways.

cell biology↗

bioRxiv2022

Plasma membrane nanodeformations promote actin polymerisation through CIP4/CDC42 recruitment and regulate type II IFN signaling

In their environment, cells have to cope with mechanical stresses constantly. Among those, nanoscale deformations of plasma membrane induced by substrate nanotopography are now largely accepted as a biophysical stimulus influencing cell behaviour and function. However, the mechanotransduction cascades involved and their precise molecular effects on cellular physiology are still poorly understood. Here, using homemade fluorescent nanostructured cell culture surfaces, we explored the role of Bin/Amphiphysin/Rvs (BAR) domain proteins as mechanosensors of plasma membrane geometry. Our data reveal that distinct subsets of BAR proteins bind to plasma membrane deformations in a membrane curvature radius-dependent manner. Furthermore, we show that membrane curvature promotes the formation of dynamic actin structures mediated by the Rho GTPase CDC42, the F-BAR protein CIP4 and the presence of PI(4,5)P2, independently of clathrin. In addition, these actin-enriched nanodomains can serve as platforms to regulate receptor signaling as they appear to contain Interferon {gamma} receptor (IFN{gamma}-R) and to lead to the partial inhibition of IFN{gamma}-induced Janus-activated tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) signaling.

cell biology↗