Are hydroxyl-containing biomolecules important in biosilicification? A model study.

To understand the roles of hydroxyl-containing biomolecules in biosilicification, theoretical and experimental studies of silica formation utilizing biological and model organic additives have been undertaken. However, the role of hydroxyl functionalized biomolecules in silica formation is still not fully understood. To address this problem, we performed a systematic in vitro study of silica formation in the presence of two proteins rich in hydroxyl-containing amino acids (native sericin proteins extracted from Bombyx mori and a recombinant sericin precursor peptide) and a range of small alkanediols. The data obtained suggest the following hypotheses for the role of hydroxyl-containing organic molecules in silica formation. In the first case, hydroxyl-containing organic molecules are not at all involved chemically in the formation of silica. Instead, they may be only assisting in rendering stability and solubility to the organic molecules found occluded in silica. The second possibility is that if we assume that hydroxyl-containing organic molecules affect silica formation, then the environments of silicic acid polymerization could be highly deficient in water to increase the effects of hydroxyl functional groups of proteins in silica formation. These results and their implications are discussed in the context of biosilicification and biomineralization.