The purified major intrinsic protein of the lens fiber plasma membrane (MP26) reconstituted into liposomes favored membrane-to-membrane close contacts as visualized by freeze fracture and immunoelectron microscopy. Reconstituted apposed unilamellar vesicles formed pentalaminar profiles, and multilamellar liposomes showed regions of stacked bilayers. Immunogold labeling, using antibody directed against MP26, demonstrated that this polypeptide is present in regions of membrane-to-membrane close interaction. Fracture faces displayed both randomly distributed clusters of 8-nm polygonal intramembrane particles and membrane domains where a bidimensional lattice of repeating subunits was present. The structural pleomorphism which characterized the MP26-reconstituted proteoliposomes seems quite comparable to that visualized in natural fiber plasma membrane domains.

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