Biotechnological Mineral Composites via Vaterite Precursors

Abstract

Vaterite is one of the thermodynamically less stable polymorphs of calcium carbonate. Under ambient conditions it transforms into calcite, the most stable form of calcium carbonate. Organisms are able to stabilize minerals such as vaterite by means of organic molecules. The exact mechanisms how biomineralization proteins interact with metastable mineral phases are, however, less well understood. Many in vitro studies were performed using calcite as a model system. A deeper understanding of the interaction of organic molecules with metastable mineral phases would make them useful as a tool to control mineralization processes in vitro. In this study, we report on the co-precipitation of a natively soluble histidine-tagged GFP (green fluorecent protein) with a metastable vaterite phase and the subsequent insolubility of the fluorescent organic matrix in a 30μl calcium carbonate precipitation assay. The intrinsic fluorescence of GFP is conserved during the interaction with the mineral phase, indicating proper folding even in the insoluble state. This experiment can be extended to obtain deeper insights into some mechanistic models of biomineralization proteins by tracking native and modified GFP proteins microscopically during various stages of mineral precipitation and dissolution.

GFP Facilitates Native Purification of Recombinant Perlucin Derivatives and Delays the Precipitation of Calcium Carbonate

“…With respect to biomineralization, no particular function was known for the green-fluorescent protein (GFP) from the non-mineralizing marine organism Aequorea victoria [32] until it was found that GFP incorporates into metastable calcium carbonate mineral phases such as vaterite while maintaining its fluorescence properties [28] . Here, we intensely characterized GFP-tagged recombinant perlucin from the abalone’s mother-of-pearl.…”

“…In a recent report, histidine-tagged GFP co-precipitated with a metastable vaterite phase and the fluorescent organic matrix became subsequently insoluble while the calcium carbonate dissolved. The intrinsic fluorescence of the protein was conserved during its interaction with the mineral phase, indicating a proper folding of GFP in its insoluble state [28]. This paper reports on perlucin derivatives in the form of GFP fusion proteins, obtained by heterologous expression in E. coli , and their interaction with calcium carbonate precipitation from solution.…”

Recombinant perlucin derivatives influence the nucleation of calcium carbonate

“…19,20 The C-terminal sequences of perlucin vary in the length of the repetitive elements, containing up to nine times "SLHANLQQRD" in a 240 amino acid precursor protein. 21,22 Both native 23 and recombinant perlucin [24][25][26] were shown to affect the crystallisation of calcium carbonate in previous in vitro assays and hence this protein is an interesting candidate for further in-depth studies of CaCO 3 nucleation and early growth behaviour. In view of the fact that perlucin has C-type lectin properties, various types of carbohydrates including chitin derivatives are likely candidates for mediating responsive perlucin interactions in vivo.…”