Biology subjects

Morsomme, P.

Publications and source records attributed to Morsomme, P..

3 recordsLinked to original sources

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↗