Lu H et al. (2021), Role of Water in CaCO3 Biomineralization.

ECB-ART-49362

J Am Chem Soc 2021 Feb 03;1434:1758-1762. doi: 10.1021/jacs.0c11976.

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Role of Water in CaCO3 Biomineralization.

Lu H , Huang YC , Hunger J , Gebauer D , Cölfen H , Bonn M .

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Biomineralization occurs in aqueous environments. Despite the ubiquity and relevance of CaCO3 biomineralization, the role of water in the biomineralization process has remained elusive. Here, we demonstrate that water reorganization accompanies CaCO3 biomineralization for sea urchin spine generation in a model system. Using surface-specific vibrational spectroscopy, we probe the water at the interface of the spine-associated protein during CaCO3 mineralization. Our results show that, while the protein structure remains unchanged, the structure of interfacial water is perturbed differently in the presence of both Ca2+ and CO32- compared to the addition of only Ca2+. This difference is attributed to the condensation of prenucleation mineral species. Our findings are consistent with a nonclassical mineralization pathway for sea urchin spine generation and highlight the importance of protein hydration in biomineralization.

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	Figure 1. (A) Titration curve of Ca2+ into 5 μM SM50-CTL protein in 10 mM carbonate buffer. Different mineralization regimes are marked: under-supersaturation (I), supersaturation (II), and nucleation into (amorphous) minerals (III).10,19,25,26 The curves for dosed Ca2+ (red) and Ca2+ titrated into Tris buffer (green) are also shown. (B) Experimental scheme illustrating the interfacial mineralization and SFG spectroscopy. Spectra reported here were recorded with S-, S-, and P-polarized SFG, visible (VIS), and infrared (IR) light, respectively.
	Figure 2. (A) Amide I SFG spectra for SM50-CTL protein at the air–carbonate buffer interface, with various amounts of Ca2+ ions indicated in the legend. The fits are shown as black lines. (B) Fitting amplitudes for two amide I bands with different amounts of Ca2+. Error bars represent the standard deviations of amplitudes.
	Figure 3. SFG spectra in the CH/OH region for SM50-CTL proteins at the interfaces of air with (A) 10 mM carbonate buffer and (B) 10 mM Tris buffer, at different, indicated Ca2+ concentrations. The spectra for pure H2O are shown for comparison.
	Figure 4. Integrated SFG intensity (A) and change of the first moment (B) of the two OH bands with adding different Ca2+ concentrations into carbonate (navy) and Tris buffer (red). The data were all fit to a single-exponential function (shown as lines). The background colors correspond to the different mineralization regimes in accordance with Figure 1A. Error bars show the standard deviations of the integrated intensities from multiple data sets.
	Figure 5. Sketch illustrating decreasing water alignment according to decreasing net charge at the SM50-CTL interface, with (center, carbonate buffer) and without (right, Tris buffer) prenucleation.

References [+] :

Avaro, Stable Prenucleation Calcium Carbonate Clusters Define Liquid-Liquid Phase Separation. 2020, Pubmed