DETECTION OF MONODISPERSE AGGREGATES OF A RECOMBINANT AMELOGENIN BY DYNAMIC LIGHT-SCATTERING

Recombinant murine amelogenins M179 and M166 were expressed in Escheri chia coli and purified. The aggregation properties of these amelogenin s have been investigated in aqueous solutions as well as acetonitrile- containing solutions using dynamic light scattering. Dynamic light sca ttering provides direct measurement of the translational diffusion coe fficient and hydrodynamic radius, and of an estimate of the molecular weight. Polydispersity and statistical parameters of how to interpret the analysis are also provided. Amelogenin aggregation was examined in solutions of a range of pH, ionic strengths, and protein concentratio ns. It was shown that at pH 7.8-8 and ionic strength of 0.02-0.05M the M179 molecules form monodispersed aggregates with hydrodynamic radii ranging from 15 to 19 nm. Analysis of hydrodynamic radii and size dist ribution of M179 aggregates in acetonitrile-containing solvents compar ed to that in aqueous solutions indicated a primary role for hydrophob ic interactions in the association process of amelogenin molecules to form aggregates. Comparison between the aggregates formed by M179 and M166, which lacks the hydrophilic carboxy-terminal 13 residue sequence of M179, suggested that the self-assembly of amelogenin molecules to form stable and monodisperse aggregates requires the presence of the h ydrophilic carboxy-terminal sequence of M179. (C) 1994 John Wiley and Sons, Inc.