Related Experiment Video
Updated: May 20, 2026
Realistic Membrane Modeling Using Complex Lipid Mixtures in Simulation Studies
Published on: September 1, 2023
Mouse TSPO in a lipid environment interacting with a functionalized monolayer
David Teboul1, Sylvie Beaufils, Jean-Christophe Taveau
1Université Paris, Denis Diderot, Paris, France.
Abstract:
Translocator protein TSPO is a membrane protein highly conserved in evolution which does not belong to any structural known family. TSPO is involved in physiological functions among which transport of molecules such as cholesterol to form steroids and bile salts in mammalian cells. Membrane protein structure determination remains a difficult task and needs concomitant approaches (for instance X-ray- or Electron-crystallography and NMR). Electron microscopy and two-dimensional crystallization under functionalized monolayers have been successfully developed for recombinant tagged proteins. The difficulty comes from the detergent carried by membrane proteins that disrupt the lipid monolayer. We identified the best conditions for injecting the histidine tagged recombinant TSPO in detergent in the subphase and to keep the protein stable. Reconstituted recombinant protein into a lipid bilayer favors its adsorption to functionalized monolayers and limits the disruption of the monolayer by reducing the amount of detergent. Finally, we obtained the first transmission electron microscopy images of recombinant mouse TSPO negatively stained bound to the lipid monolayer after injection into the subphase of pre-reconstituted TSPO in lipids. Image analysis reveals that circular objects could correspond to an association of at least four monomers of mouse TSPO. The different amino acid compositions and the location of the polyhistidine tag between bacterial and mouse TSPO could account for the formation of dimer versus tetramer, respectively. The difference in the loop between the first and second putative transmembrane domain may contribute to distinct monomer interaction, this is supported by differences in ligand binding parameters and biological functions of both proteins.
Insights
Researchers visualized the mouse translocator protein TSPO using electron microscopy. They determined TSPO forms tetramers, offering insights into its structure and function in cholesterol transport.
Area of Science:
- Structural biology
- Membrane protein research
- Biochemistry
Background:
- Translocator protein (TSPO) is a conserved membrane protein with vital roles in cholesterol transport and steroidogenesis.
- Determining membrane protein structures is challenging due to their hydrophobic nature and reliance on detergents.
- Existing methods like X-ray crystallography and NMR have limitations for certain membrane proteins.
Purpose of the Study:
- To determine the oligomeric state and structure of recombinant mouse TSPO using transmission electron microscopy (TEM).
- To establish a method for stabilizing and visualizing detergent-solubilized membrane proteins on functionalized monolayers.
- To investigate potential structural differences between bacterial and mouse TSPO and their implications for function.
Main Methods:
- Utilized electron microscopy and 2D crystallization on functionalized monolayers.
- Developed optimal conditions for injecting histidine-tagged recombinant TSPO in detergent into a subphase.
- Reconstituted TSPO into lipid bilayers to facilitate adsorption and minimize detergent disruption.
- Employed negative staining TEM for imaging.
Main Results:
- Successfully obtained the first TEM images of recombinant mouse TSPO bound to a lipid monolayer.
- Image analysis indicated the formation of circular structures consistent with tetramers (association of at least four monomers).
- Observed potential differences in oligomerization (dimer vs. tetramer) between bacterial and mouse TSPO, linked to amino acid composition and tag location.
Conclusions:
- The study provides the first structural evidence of mouse TSPO forming tetramers.
- The developed method allows for the structural analysis of detergent-bound membrane proteins.
- Differences in TSPO structure may explain variations in ligand binding and biological functions across species.
