Dynamics and nanoenvironment of biological membranes


(Aix-Marseille Université & INSERM)

Overview

We are an interdisciplinary research unit with an important international openness and direct collaboration between cell biologists, biochemists and biophysicists.

We are combining classical biochemical and cell biology approaches with the development of new force microscopy nanotools to map the dynamics, interactions and mechanics of the cell membrane and its nanoenvironment. 

This interdisciplinary approach is developed at different scales, from the nanoscale of proteins and membranes to the microscale of cells and tissues, and at different timescales, from microseconds to minutes. 

Research lines

Dynamics and interactions of the cell membrane and its nanoenvironment

Dynamics of membrane proteins and membrane remodeling, in health and disease 

We are aiming to understand how proteins and lipids interact to drive membrane deformation, fusion and fission and how the mosaic membrane generates complexity and biological function. We are investigating minimal in vitro reconstituted systems to precisely evaluate the biophysical aspects and the physical chemistry of lipid membranes and protein assemblies. In particular, we are studying the effect of antimicrobial peptides on bacterial membranes (with an eye on pharmaceutical applications), calcium-triggered exocytosis, dynamics voltage-gated ion channels and in situ conversion of ceramides altering membrane composition. 


Protein-protein and protein-lipid interactions of neuronal synapse 

At neuronal membranes, several cis and trans protein-protein and protein-lipid interactions take place and play important roles in neuronal physiology. Our interest focuses on (1) neuronal receptors of botulinum neurotoxin and (2) the secreted LGI1 (Leucin-rich Glioma inactivated 1).

(1) Botulinum neurotoxins are widely used therapeutic agents that interact membrane-exposed protein/lipid double receptors involving two distinct synaptic proteins synaptotagmin and SV2. Our data suggest that these interactions are necessary for botulinum neurotoxin binding. Synaptotagmin isoforms 1 and 2, the principal Ca2+-sensors for exocytosis, abundantly expressed in synaptic vesicles at most nerve terminals and target for autoantibodies that occur in immune-mediated Lambert-Eaton myasthenic syndrome. We aim at understanding the physiological importance of synaptotagmin as well as SV2/gangliosides interaction in neuronal physiology and address the detailed molecular parameters of botulinum neurotoxins binding and translocation through membranes.

(2) LGI1 is a secreted glycoprotein involved in the control of neuronal excitability and implicated in human pathology. The absence of LGI1 secretion or its targeting by autoimmune antibodies lead to an important change in a class of potassium channels (Kv1) expression known to be enriched in specific lipid nanodomains. How an extracellular protein modulates Kv1 membrane stability is unknown. Recently, we discovered that LGI1 interacts with brain gangliosides and we postulate that, by this interaction, LGI1 may organize lipid domains that traps Kv1 channels. We will dissect the implication of LGI1 in preparing such membrane domains.


Single molecule interaction and membrane mechanics

The interaction of the membrane proteins with the cytosolic and extracellular nanoenvironment is mediated by individual molecules. We are probing the interaction of protein-protein and membrane-protein interaction using single molecule force spectroscopy with AFS and AFM. These measurements are complemented with bulk, ensemble measurements with surface plasmon resonance. In addition, the mechanical response of membranes modulates membrane and membrane protein dynamics. We are using similar approaches to better understand the mechanics of membranes over a wide range of timescales.


Biological physics and mechanobiology of cells and tissues in health and disease

Multiscale adhesion and mechanics in cell function

Adhesion and mechanics are interrelated and difficult to understand one without the other. We are studying the interplay between adhesion and mechanics involved in two specific biological processes: cancer cell malignancy and the leukocyte adhesion cascade. Cancer cell malignancy implies formation of metastases and it is known that malignancy correlates with cell softness, in turn modulated by the interaction with the nanoenvironment. The leukocyte adhesion cascade is the first response of the immune system and a highly mechanical process, involving adhesion of leukocytes to the vascular endothelium through single molecules, the formation of long membrane tethers and the deformation and reorganization of the cell cytoskeleton. Complete understanding of the physics behind these two processes requires an approach over multiple length and time scales, from single molecules to the whole cell. Our approach involves mechanical measurements at multiple length and time scales: probing the binding strength of single adhesion complexes and unfolding of proteins, as well as the membrane deformation and tether formation and cytoskeleton microrheology across the cell surface, from microseconds to minutes and hours. 

Cancer stem cells and microenvironment mechanics

Although overlook for a while, the relevance of mechanical cues for the cell fate and normal functions is now widely admitted. This research line involves stem cells and their pathological counter-part responsible of cancer (cancer stem cells, CSCs). Recent works suggest that mechanical properties of the microenvironment exert a crucial role in stemness maintenance. This raises a genuine new field of investigation, rheo-histology, that will provide new information about tissue organization and function adding a new dimension beyond the 3D-space. 

Fundamental mechanical response of single molecules, membranes, cells and tissues 

Mechanics of cells and tissues play a crucial role in many cell functions. Cells and tissues are complex materials that, as such, have a complex, heterogeneous viscoelastic response. The development of advance tools to better probe cell and tissue mechanics at the nanometre and micrometre scales and over the wider dynamic regime is thus essential to understand the role of mechanics in cell function. Moreover, knowledge of the mechanical response of their molecular components such as membranes and single protein filaments, is crucial to obtain a mechanistic description. We developed new techniques, approaches, models and protocols to more robustly and accurately probe cell and tissue rheology and the membrane and single molecule mechanics. Our work is based on nanotools available in the laboratory, mainly atomic force microscopy (AFM) and acoustic force spectroscopy (AFS). This is complemented with other approaches available through collaboration or accessible to the lab such as traction force microscopy, optical tweezers, nanoindentation and cell and tissue stretchers. 

Nanotechnology innovation

A strong and unique capacity of our lab is the innovation, development and application of nanotechnology tools. Importantly, atomic force microscopy techniques complemented with traditional approaches. In particular, we are one of the pioneer laboratories of high-speed atomic force microscopy (HS-AFM) and high-speed force spectroscopy (HS-FS), a unique nanotool that allows label-free imaging of the dynamics of molecular processes at the nanoscale and is capable of probing the mechanics of biomolecules, membranes and cells with microsecond time resolution.

More recently, we have implemented acoustic force spectroscopy (AFS) to probe single molecule receptor-ligand interactions at low loading rate and mechanics of living cells at low frequencies. 

Selected Publications

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Address:

DyNaMo U1325, INSERM & Aix-Marseille Unviersité

Parc Scientifique de Luminy, Bâtiment Inserm TPR2 bloc 5, case 909

163 avenue de Luminy, 13009 Marseille, France