Importance of electrostatic interactions between calcite surfaces and proteins

We have studied the electrostatic interactions of proteins with the calcite surfaces during its subsequent nucleation and growth on a surface. In doing so, a model system of four globular proteins (lysozyme, ribonuclease, myoglobin and alpha-lactalbumin), having the same size and conformation, but differing in surface properties (i.e. surface charge) was used. Depending on the nature of the charge on the protein, its morphological effect on calcite growth (inhibition of specific crystal faces) varies, with this effect becoming more pronounced as the protein is more negatively charged. To study how the adsorption of proteins affects the growth of calcite along different crystal directions, calcite plates cut with different crystallographic orientations (i.e. (001), (104), (100) and (110)) were used as substrates. The overgrowing calcite crystals show the same orientation as the substrate. The nucleation density also varies with the crystallographic orientation of the calcite substrates, increasing in accordance with the sequence: (110), (100) and (001). Finally, to study how the protein itself controls the orientation of crystals, we used amorphous substrates (glass). After incubation on the glass substrates with negatively charged proteins, an oriented nucleation of the calcite crystals was induced.