Department of Chemistry, University of the Ryukyus, Okinawa, Japan.
Connect Tissue Res. 2009;50(5):285-93.
Acidic proteins are generally thought to control mineral formation and growth in biocalcification. Analysis of proteinaceous components in the soluble and insoluble matrix fractions of sclerites in Sinularia polydactyla indicates that aspartic acid composes about 60% of the insoluble and 29% of the soluble matrix fractions. We previously analyzed aspartic acids in the matrix fractions (insoluble = 17 mol%; soluble = 38 mol%) of sclerites from a different type of soft coral, Lobophytum crassum, which showed comparatively lower aspartic acid-rich proteins than S. polydactyla. Thus, characterization of highly acidic proteins in the organic matrix of present species is an important first step toward linking function to individual proteins in soft coral. Here, we show that aspartic-acid rich proteins can control the CaCO(3) polymorph in vitro. The CaCO(3) precipitates in vitro in the presence of aspartic acid-rich proteins and 50 mM Mg(2+) was verified by Raman microprobe analysis. The matrix proteins of sclerites demonstrated that the aspartic-acid rich domain is crucial for the calcite precipitation in soft corals. The crystalline form of CaCO(3) in the presence of aspartic acid-rich proteins in vitro was identified by X-ray diffraction and, revealed calcitic polymorphisms with a strong (104) reflection. The structure of soft coral organic matrices containing aspartate-rich proteins and polysaccharides was assessed by Fourier transform infrared spectroscopy. These results strongly suggest that the aspartic acid-rich proteins within the organic matrix of soft corals play a key role in biomineralization regulation.
酸性蛋白通常被认为控制生物矿化过程中的矿物质形成和生长。对鹿角珊瑚（Sinularia polydactyla）中硬骨组织可溶性和不溶性基质部分的蛋白成分进行分析表明，天冬氨酸约占不溶性基质的 60%和可溶性基质的 29%。我们之前对另一种软珊瑚（Lobophytum crassum）的硬骨组织基质部分（不溶性=17mol%；可溶性=38mol%）中的天冬氨酸进行了分析，结果表明其富含天冬氨酸的蛋白比鹿角珊瑚中的含量要低。因此，对目前这一物种的有机基质中高度酸性蛋白进行特征描述是将功能与软珊瑚中特定蛋白联系起来的重要第一步。在此，我们证明了富含天冬氨酸的蛋白能够在体外控制碳酸钙多晶型。通过拉曼微探针分析证实，在富含天冬氨酸的蛋白和 50mM Mg2+存在的情况下，体外能够产生碳酸钙沉淀。硬骨组织的基质蛋白表明，富含天冬氨酸的结构域对软珊瑚中碳酸钙的沉淀起着关键作用。体外含有富含天冬氨酸蛋白的碳酸钙的晶体形态通过 X 射线衍射进行了鉴定，并揭示了具有强（104）反射的方解石多晶型。通过傅里叶变换红外光谱评估了含有富含天冬氨酸蛋白和多糖的软珊瑚有机基质的结构。这些结果强烈表明，软珊瑚有机基质中的富含天冬氨酸蛋白在生物矿化调节中发挥着关键作用。
