Membrane-bound protein in giant vesicles: induced contraction and growth

Cell-sized giant vesicles, produced by electroformation, were composed of phospholipids and zein (a hydrophobic protein that occupied a substantial percentage of the vesicle surface). Addition of sodium dodecyl sulfate removed the protein into the bulk phase, which led to a shrinkage of the vesicles. The vesicle bilayers were able to heal themselves from the damage caused by the departure of the zein, allowing the bilayers to maintain their spherical morphology. Giant vesicle growth was also observed when the following components were mixed (all four being necessary): (a) negatively charged giant vesicles, (b) membrane-incorporated zein, (c) positively charged submicroscopic vesicles (almost 103 times smaller than the giant vesicles), and (d) sodium dodecyl sulfate. The simplest mechanism consistent with literature data involves electrostatically promoted binding of the small vesicles (weakened by the surfactant) onto the giant vesicle surface, followed by the merging of membranes at protein-induced "fusion hot spots". The "feeding" of small vesicles by giant vesicles then leads to growth.