Protein-mediated Intermembrane Contact Facilitates Fusion of Lipid Vesicles with Planar Bilayers

Fusion of phospholipid vesicles with planar bilayer membranes occurs provided there is an intermembrane contact, which can be mediated by phospholipid-binding proteins, even in the absence of calcium. The firm attachment phase is then followed by the osmotically-driven fusion. These results show that hydrophobic proteins (not necessarily Ca2+-binding proteins) may enhance fusion by promoting contact of membranes. Such proteins may operate synergistically with Ca2+ to reduce the threshold concentration of Ca2+ needed for fusion of biological membranes. Protein-mediated intermembrane contact resulting in fusion may play a crucial role in the regulation and catalysis of biological fusion events.