FOOD MUSTARD ALLERGEN INTERACTION WITH PHOSPHOLIPID-VESICLES

Sin a I, the major allergen from mustard seeds, interacts with acid phospholipid vesicles. The protein binds to dimyristoylglycerophosphoglycerol vesicles with an apparent dissociation constant of approximately 2.4 mu M, the number of phospholipid molecules affected by one protein molecule being approximately 20. Sin a I promotes an increase in the light scattering of a vesicle suspension. This process becomes saturated at approximately a lipid/protein molar ratio of 20:1. Sin a I also modifies the thermotropic behaviour of the negatively charged vesicles, which has been studied by measuring the fluorescence polarization of the probe 1,6-diphenyl-1,3,5-hexatriene incorporated into the hydrophobic core of the bilayer. Sin a I also promotes lipid mixing between vesicles. This mixing has been analyzed by measuring the variation of the fluorescence energy transfer between N-(7-nitro-2-1,3-benzoxadiazol-4-yl)-dimyristoylglycerophosphoethanolamine (donor) and N-(liss-amine rhodamine B sulphonyl)-PtdEtn (acceptor) incorporated into dimyristoylglycerophosphoglycerol vesicles. This effect is also corroborated by observing a single thermotropic transition in a mixture of independent dipalmitoylglycerophosphoglycerol and dimyristoylglycerophosphoglycerol vesicles when Sin a I is added to the lipid suspension. The allergen promotes release of aqueous contents of PtdGro vesicles, as determined by an aminonaphthalenetrisulfonic acid/p-xylylenebis(pyridinium)bromide dequenching assay. This study shows that the allergen Sin a I is able to interact with membrane lipids. This interaction is dicussed in terms of its potential involvement in the allergenicity of this protein.