TEMPERATURE AND PH-DEPENDENT SUPRAMOLECULAR SELF-ASSEMBLY OF AMELOGENIN MOLECULES - A DYNAMIC LIGHT-SCATTERING ANALYSIS

Evidence for the molecular self-assembly of amelogenin proteins to for m quasi-spherical particles (''nanospheres'') in solution, both in vit ro and in vivo, has recently been documented. A particle-size distribu tion analysis of dynamic light-scattering data was undertaken to inves tigate the influence of temperature on this molecular self-assembly pr ocess at three different pH's. The long-term objective was to correlat e these observations to the unusual physiochemical characteristics of the protein, to improve understanding of the molecular mechanisms invo lved in the generation of amelogenin ''nanospheres'' and understanding of their putative relation to amelogenin function in vivo. We analyze d data using two different algorithms: Dynamics and DynaLS. It was fou nd that at pH 8, in a temperature range between 5 and 25 degrees C, th e size of the recombinant amelogenin nanospheres is monodisperse, givi ng rise to particles of 15-18 nm in hydrodynamic radius. However, hete rogeneous distribution of particle size was observed at temperature ra nges between 27 and 35 degrees C, becoming monodisperse again with lar ger particles (60-70 nm) after the temperature was elevated to 37-40 d egrees C. We interpret these results to suggest that amelogenin molecu lar self-association possesses a second stage assembly process at temp eratures of 30-35 degrees C, creating larger entities which apparently are structured and stable at 37-40 degrees C. The effect of pH on the size of amelogenin ''aggregates'' was much more noticeable at 37 degr ees C compared to that at 25 degrees C. This observation suggests that at physiological temperature (i.e., 37 degrees C) amelogenin molecula r self-assembly is extremely sensitive to pH changes. This finding sup ports the notion that local pH changes in the microenvironment of the enamel extracellular matrix may play critical roles in controlling the structural organization of the organic matrix framework. (C) 1998 Aca demic Press.