Does Amelogenin Nanosphere Assembly Proceed through Intermediary-sized Structures?

Abstract

Previous studies have demonstrated the presence of supra-molecular assemblages of amelogenin protein (“Nanospheres”) to be present in both in vivo and in vitro situations. We have proposed that these nanosphere structures are functionally involved in the organization and control of initial enamel biomineralization at the ultrastructural level. Based on the observed nanosphere hydrodynamic radii (18–20nm diameter) computation suggests these structures to be compounded of some 100 amelogenin monomers, raising the question as to the possible molecular mechanism for the assembly of such structures? Based on recent dynamic light scattering experiments using the recombinant murine amelogenin M179, and employing a newer size distribution algorithm we now report that the size distribution data for M179 are better described by a bimodal distribution model, than the monomodal distribution as previously described. We suggest that amelogenin nanosphere assembly proceeds through intermediate structures (perhaps represented in vivo by “stippled material”) of some 4–5 nm hydrodynamic radius, and computed to comprise 4–6 amelogenin monomers. We suggest that such intermediary, sub-unit structures, assemble through inter-molecular hydrophobic interactions to generate the 20nm diameter nanospheres observed by TEM in the secretory stage enamel matrix.