Protein-mineral interactions at the organic-inorganic interface in biominerals

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Bones, teeth, otoconia, eggshells, snail shells, sea shells, corals, and many other biomineralized structures arise from synergistic interactions between co-existing organic (usually proteins) and inorganic mineral (often calcium-based) phases. These interactions produce hard, composite biological materials having specialized properties, largely attributable to hierarchically organized, supramolecular assemblies that provide a framework for remarkable biomineralized architectures. Negatively charged proteins within this organic framework (the extracellular matrix) may stabilize amorphous mineral precursor phases, or they may attain regulatory chemical complementarity by binding to lattice calcium at the organic-inorganic interface - mechanisms that influence crystal growth processes. It is hypothesized that the molecular precision of such organic-inorganic interfacial interactions regulates crystal growth to produce such hardened, biomineralized composite structures. My NSERC DG biomineralization research program focuses on specific biomolecules and proteins/peptides (notably osteopontin) that regulate calcium carbonate mineral growth (specifically here, the forms calcite and vaterite). Small biomolecules, amino acids, peptides and full-length proteins guide and regulate biomineralization. A common theme for calcium carbonate mineralization is that nanoparticles form within a confined, protein/peptide-rich reaction nanoenvironment, from which they crystallize and align over many length scales to build mesocrystals having occluded organics. This notion contrasts with classical crystallization theory which postulates ion-by-ion attachment. My biomineralization research program compares these scenarios by exploring fundamental principles of how relevant organics influence biomineralization. The short-term objectives for this proposal are to continue examining the extracellular regulatory mechanisms guiding Ca-carbonate biomineralization through three projects: i) reptile (gecko and snake) eggshell structure, ii) the interface (attachment) of avian and reptilian eggshell membrane fibers with the mineral of the shell, and iii) the determinants of synthetic, chiral helicoidal vaterite suprastructure growth (including simulations). Long-term objectives are to explore i) how diverse biomolecules influence Ca-carbonate growth and hierarchical assembly, and ii) how biomineral curvature (vs angulated facets) is produced in biology, particularly in shells. With new information from this research, we will understand key elements of biomineralization biology for calcium carbonate (particularly in eggshells, with implications for food safety in the case of the table egg) that might well cross over into other biomineralizing systems. Such a cross-over may potentially allow for tunable mineralization events in synthetic biomaterials with uses in tissue repair and tissue engineering applications, and for novel chiral materials with unique optical properties.