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 form quasi-spherical particles ("nanospheres") in solution, both in vitro and in vivo, has recently been documented. A particle-size distribution analysis of dynamic light-scattering data was undertaken to investigate the influence of temperature on this molecular self-assembly process at three different pH's. The long-term objective was to correlate these observations to the unusual physiochemical characteristics of the protein, to improve understanding of the molecular mechanisms involved in the generation of amelogenin "nanospheres" and understanding of their putative relation to amelogenin function in vivo. We analyzed data using two different algorithms: Dynamics and DynaLS. It was found that at pH 8, in a temperature range between 5 and 25 degrees C, the size of the recombinant amelogenin nanospheres is monodisperse, giving rise to particles of 15-18 nm in hydrodynamic radius. However, heterogeneous distribution of particle size was observed at temperature ranges between 27 and 35 degrees C, becoming monodisperse again with larger particles (60-70 nm) after the temperature was elevated to 37-40 degrees C. We interpret these results to suggest that amelogenin molecular self-association possesses a second stage assembly process at temperatures of 30-35 degrees C, creating larger entities which apparently are structured and stable at 37-40 degreesC. The effect of pH on the size of amelogenin "aggregates" was much more noticeable at 37 degrees C compared to that at 25 degrees C. This observation suggests that at physiological temperature (i.e., 37 degrees C) amelogenin molecular self-assembly is extremely sensitive to pH changes. This finding supports 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.