Enamel extracelluar matrix components play vital roles in controlling crystal nucleation and growth during enamel formation. We investigated the interaction between the 32 kDa enamelin fragment and amelogenin using immunochemical and biophysical methods. Immunoprecipitation studies revealed that the 32 kDa enamelin and amelogenin eluted together from a Protein A column. Dynamic light scattering results showed that the 32 kDa enamelin had a profound effect on amelogenin assembly at pH 8.0, causing partial dissociation of the nanospheres, in a dose-dependent manner. The appearance of an isodichroic point and the shifting and intensity decrease of the ellipticity minima in the circular dichroism spectra of amelogenin following the addition of the 32 kDa enamelin were indicative of conformational changes in amelogenin and of a direct interaction between the two macromolecules. Our results collectively demonstrate that the 32 kDa enamelin has a direct interaction with amelogenin in vitro. Our current studies provide novel insights into understanding possible cooperation between enamelin and amelogenin in macromolecular self-assembly and in controlling enamel mineral formation. (C) 2009 Elsevier Inc. All rights reserved.