Vesicle Adhesion and Fusion Studied by Small-Angle X-Ray Scattering

Area of Science:

• Biophysics
• Materials Science

Background:

• Lipid vesicle adhesion is crucial for biological processes.
• Understanding ion-induced interactions is key to controlling membrane behavior.

Purpose of the Study:

• To investigate the adhesion and structural changes of lipid vesicles induced by divalent ions (Ca2+, Mg2+).
• To analyze the role of lipid composition and charge density in ion-mediated vesicle interactions.
• To explore the potential for using small-angle x-ray scattering (SAXS) for studying protein-controlled docking.

Main Methods:

• Small-angle x-ray scattering (SAXS) was used to analyze bilayer structure and interbilayer distances.
• Controlled experiments with varying ion concentrations, lipid compositions (DOPC:DOPS, pure DOPS), and charge densities were performed.
• Reconstituted N-ethylmaleimide-sensitive factor attachment protein receptors (N-ERs) in proteoliposomes were characterized using SAXS.

Main Results:

• Divalent ions induced a strong adhesion state in DOPC:DOPS vesicles, consistent with ion correlation-driven like-charge attraction.
• Observed interbilayer separations of ~1.6 nm quantitatively matched electrostatics predictions in the strong coupling regime.
• Pure anionic DOPS membranes exhibited a phase transition to a multilamellar state, suggesting vesicle rupture and fusion.

Conclusions:

• Ion correlations play a significant role in inducing lipid vesicle adhesion, even with like charges.
• Lipid charge density is a critical factor determining the outcome of ion-induced membrane interactions, leading to adhesion or fusion.
• SAXS is a valuable technique for structural analysis of both ion-induced and protein-mediated membrane events.