Ricin A-chain induces fusion of small unilamellar vesicles at neutral pH

Abstract
The interaction of ricin and its constituent polypeptides, the A- and B-chain, with small unilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) or dimyristoylphosphatidylcholine (DMPC) was investigated by means of differential scanning calorimetry measurements. The A-chain, at neutral pH, entirely shifted the endothermic peak of small unilamellar vesicles of DPPC from 37°C to 41°C at low protein/lipid ratios. The potency of either ricin or the B-chain to induce the shift of endothermic peak was much less than that of the A-chain. The A-chain was also found to cause mixing of endothermic peaks of DMPC vesicles and DPPC vesicles. These data strongly suggest that the A-chain has the ability to induce fusion of phospholipid vesicles.