Gliadin effect on giant vesicle elastic modulus

摘要

Wheat gluten consists of a complex supramolecular protein assembly of very high molecular mass, with over a million daltons, that displays important viscoelastic and interfacial properties. Its involvement in an immunologically based nutritional disease, the celiac disease, is thought to be somehow related to nontrivial structural features of the protein complex, apparently involving gliadin, one of its fractions. Despite its medical relevance, the involvement of gliadin in the etiology of the celiac disease is nevertheless not understood in terms of the mechanisms involved. In this context, gliadin was investigated relative to its effect on fluid bilayer elasticity. Dioleoylphosphatidylcholine giant unilamellar vesicles (about 50-μm diameter) were produced by electric field pulsing over metal-covered plates. The technique of micropipette suction allowed vesicle invagination into a micropipette by applying a suction pressure. A video camera coupled to a microscope permitted the suction process to be monitored and the different relevant geometric quantities to be measured: vesicle projection length into the pipette, for different applied pressures; vesicle and pipette diameters. The vesicle projection length into the pipette as a function of pressure, for a given vesicle and pipette diameter, is related to the bilayer bending modulus k_c. Assayed samples comprised vesicles with and without ethanol-dissolved gliadin incorporated in the membrane, at two distinct gliadin/phospholipid mass fractions. We observed a significant increase in k_c of the phospholipid bilayer with the largest gliadin content (0.02 gliadin/dioleoylphosphaditylcholine w/w), from about k_c = 21 k_BT, to k_c = 52 k_BT, where k_BT is the thermal energy of the solution. The results reveal the affinity between the protein and the bilayer, suggesting possible correlations between membrane mechanical properties and the celiac disease etiology.