Recombinant production of a shell matrix protein in Escherichia coli and its application to the biomimetic synthesis of spherulitic calcite crystals

Objectives To overcome the limited production capability of shell matrix proteins and efficiently conduct in vitro CaCO3 biomineralization studies, a putative recombinant shell matrix protein was prepared and characterized. Results A glycine-rich protein (GRP_BA) was found in Pinctada fucata as a putative shell matrix protein (NCBI reference sequence; BAA20465). It was genetically redesigned for the production in Escherichia coli. The recombinant protein was obtained in a 400 ml shake-flask culture at approx. 30 mg l(-1) with a purity of > 95 %. It efficiently formed a complex with Ca2+. Ca2+-induced agglomeration was like other calcification-related proteins. Spherulitic calcite micro-particles, 20-30 A mu m diam. with rosette- and sphere-like structures were synthesized in the presence of the recombinant shell protein, which could be formed by stacking and/or aggregation of calcite nanograins and the bound protein. Conclusions Recombinant production of a shell matrix protein could overcome potential difficulties associated with the limited amount of protein available for biomineralization studies and provide opportunities to fabricate biominerals in practical aspects.