Recombinant production and biochemical characterization of a hypothetical acidic shell matrix protein in Escherichia coli for the preparation of protein-based CaCO3 biominerals

Abstract

The biological structure of shells consists of highly organized calcium carbonate (CaCO3) crystals, which have remarkable mechanical and biological properties compared to the pure mineral form of CaCO3. It has been known that the organization of these biominerals is controlled by a relatively tiny amount of organic components such as shell matrix proteins. Here, we successfully produced a recombinant hypothetical acidic shell matrix protein in Escherichia coli, although the protein is composed of highly repetitive and biased amino acid sequences. About 15mg/L purified protein with greater than 95% purity was obtained in the 400 mL lab scale flask culture. The protein was able to efficiently form a complex with calcium ions, and spherulitic calcite crystals were synthesized in the presence of the recombinant protein. We expect that biomineralization using the recombinant protein could not only overcome the limited amount of protein available for biomineralization studies and biomineral preparation in practical aspects, but also provide opportunities to enable biomimetic synthesis of notable bio-composites based on organic-inorganic complexation.