DESCRIPTION (provided by applicant): Deciphering structure/function relationships underpins the acquisition of biomedical knowledge while providing the basis to create novel materials and drugs. A powerful tool for deciphering structure/function outcomes has been germline genetic manipulation in mice. In this application, we apply germline manipulation to link structure to function for the enamel matrix protein ameloblastin. Enamel is a composite bioceramic tissue with unique material properties that are owed to its mode of biological fabrication. Ameloblast cells create an extracellular enamel protein matrix that serves to control both crystallite habit and the organization of crystallite bundles, allowing thousands of nanoscale crystallites to be organized and grouped together under the control of a single cell. We hypothesize that the grouping and organization of the nanocrystallites by a single ameloblast cell is the outcome achieved by the function(s) of critical domain(s) within the ameloblastin protein. The ameloblastin protein has been described as being organized into at least two domains, an N'- and a C'- terminal domain [Iwata et al. '07], based on the finding that following cleavage the N'- and C'- ameloblastin domains are no longer found in the same physical site in the enamel rod. The N'-terminus is enriched around the rod boundaries, much as a sheath covers a knife blade, while the C'-terminal domain behaves quite differently. We hypothesize that the N'-terminus of ameloblastin is likely responsible for the cell-to-matrix interactions that maintain the highly patterned rod-to-interrod boundaries observed in enamel. We hypothesize that the C'-terminus is responsible for the protein-to-mineral interactions producing the enamel bioceramic tissue. Outcomes will be measured by changes to stereotypic enamel architecture and by analysis of the material properties of the enamel in the knockin condition compared to wildtype animals. The outcomes from this experimental strategy will contribute to our understanding of functional genomics and proteomics while furthering our understanding of the formation of the only ectoderm-derived biomineralized tissue in the vertebrate body. Preliminary data from our research team suggest that this knockin approach will yield novel insights into the structure/function relationship for the ameloblastin protein, the second most abundant protein contributing to enamel organic matrix assembly and biomineralization.

The function(s) for the second most abundant protein of the forming mammalian enamel matrix is not known. Here, we map the function(s) of ameloblastin protein domains to the production of the enamel matrix required to control enamel biomineralization. In performing this project we will create an animal model useful to study caries, the most prevalent-, infectious-disease of humankind and provide one more design specification for creating an enamel biomimetic, useful for restoring enamel lost to trauma and disease.