Dynamics of membrane nanotubes coated with I-BAR

Area of Science:

• Cell Biology
• Biophysics
• Membrane Dynamics

Background:

• Membrane deformation is crucial for cellular processes like filopodia formation.
• Proteins with membrane-binding domains, such as the IRSp53-MIM family, are involved in shaping membranes.
• Reconstituted membranes demonstrate that membrane-shaping domains can induce tubulation independently.

Purpose of the Study:

• To investigate the membrane-shaping capabilities of the I-BAR domain from the ABBA protein.
• To characterize the structural properties (diameter, stiffness) of nanotubes formed by the I-BAR domain.
• To understand the dynamics and membrane curvature preference of the I-BAR domain.

Main Methods:

• Utilized Giant Unilamellar lipid Vesicles (GUVs) to study I-BAR domain interactions.
• Employed simultaneous quantification of tube intensity and shape to determine nanotube properties.
• Conducted fluorescence bleaching experiments to assess I-BAR mobility and its correlation with tube dynamics.

Main Results:

• The ABBA protein's I-BAR domain formed semi-flexible nanotubes protruding into GUVs.
• Quantified nanotube diameter at approximately 50nm, with no significant stiffening compared to protein-free tubes.
• Observed that high I-BAR density led to immobile tubes, while lower densities allowed free diffusion.
• Demonstrated that I-BAR upconcentrates in protruding tubes at low densities, indicating a preference for negative curvature.

Conclusions:

• The I-BAR domain effectively deforms lipid membranes into nanotubes.
• I-BAR decorated nanotubes exhibit specific diameters and flexibility, independent of protein stiffening.
• I-BAR domain mobility on the membrane influences nanotube dynamics.
• The I-BAR domain shows a strong preference for negatively curved membrane regions, suggesting a role in specific cellular membrane remodeling events.