We have observed by atomic force microscopy that an interdigitated liquid disordered domain (ILDD) is formed in the ganglioside (GM1)/sphingomyelin (SM)/cholesterol (CHOL) bilayers on a mica surface and accelerates the formation of fibriller A beta agglomerates. By studies of the mechanisms using molecular dynamics simulations, we conclude that the ILDD structure is formed as a result of the phase separation to SM- and GM1-rich domains on the mica surface induced by the effects of GM1 clustering and the interaction between the GM1 head group and the water layer adsorbed in the ditrigonal cavity on the mica surface. (C) 2010 Elsevier B.V. All rights reserved.