Production and Characterization of Recombinant Amelogenin Phosphorylation Mimics

Abstract: Amelogenin is an extracellular matrix protein which has an important role to play in enamel formation during tooth development. The need for amelogenin for research purposes in order to be utilized for its many potential applications have resulted in the rise of the production of recombinant amelogenin. So far, the most optimal expression system used for the production of recombinant amelogenin is Escherichia coli. The only difference between native amelogenin and recombinant amelogenin expressed using E.coli is that the latter lack methionine at the N-terminus and phosphate on Serine-16.The aim of this study was to produce recombinant amelogenin phosphorylation mimics and to investigate the effects of phosphorylation on amelogenin. A total of 16 recombinant amelogenin phosphorylation mimics were successfully constructed by site-directed mutagenesis where serine-16 was mutated to either aspartic acid or glutamic acid. There were difficulties encountered during the purification of the higher positively charged recombinant amelogenin phosphorylation mimics which indicated that factors other than optical density may have a vital effect on their production. No effect of phosphorylation was found on solubility as the phosphorylated amelogenins shared similar solubility profiles to their non-phosphorylated analogues on the pH range of 4 to 8. The solubility of the recombinant amelogenin fusion and phosphorylation mimics were greater than that of the recombinant native amelogenin and its phosphorylation mimic analogue. The analysis of the recombinant amelogenin phosphorylation mimics by dynamic light scattering showed that they too can form nanospheres. There were minor variations in hydrodynamic radii and polydispersity indices of the recombinant phosphorylated and non-phosphorylated amelogenins at both 20oC and 37oC which indicated that phosphorylation had not affected amelogenin self-assembly. It was found that the recombinant amelogenin phosphorylation mimics as well as their non-phosphorylated analogues had similar strong apatite-binding affinity which also showed no effect of phosphorylation on the binding affinity of amelogenin.