Membrane Fusion Mediated by Non-covalent Binding of Re-engineered Cholera Toxin Assemblies to Glycolipids

Membrane fusion is essential for the transport of macromolecules
and viruses across membranes. While glycan-binding proteins (lectins)
often initiate cellular adhesion, subsequent fusion events require
additional protein machinery. No mechanism for membrane fusion arising
from simply a protein binding to membrane glycolipids has been described
thus far. Herein, we report that a biotinylated protein derived from
cholera toxin becomes a fusogenic lectin upon cross-linking with streptavidin.
This novel reengineered protein brings about hemifusion and fusion
of vesicles as demonstrated by mixing of fluorescently labeled lipids
between vesicles as well as content mixing of liposomes filled with
fluorescently labeled dextran. Exclusion of the complex at vesicle–vesicle
interfaces could also be observed, indicating the formation of hemifusion
diaphragms. Discovery of this fusogenic lectin complex demonstrates
that new emergent properties can arise from simple changes in protein
architecture and provides insights into new mechanisms of lipid-driven
fusion.