Li Sicheng, Liu Xinlu, Zheng Zehua, Oshima Keisuke, Zhu Lingxiao, Kato Yugo, Negishi Lumi, Kurumizaka Hitoshi, Okumura Taiga, Nagata Koji, Pokroy Boaz, Suzuki Michio
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
Bone Marrow Transplantation Center, The First Affiliated Hospital & Liangzhu Laboratory, Zhejiang University School of Medicine, Hangzhou 311121, China.
Proc Natl Acad Sci U S A. 2025 Jul 29;122(30):e2503336122. doi: 10.1073/pnas.2503336122. Epub 2025 Jul 22.
Aragonite, a polymorph of calcium carbonate (CaCO), exhibits enhanced mechanical properties due to crystal defects such as twins, which are particularly prevalent in biogenic aragonite and can inhibit crack propagation. Despite the importance, the molecular mechanisms responsible for the formation of aragonite {110} twins in marine organisms have remained poorly understood. Identifying a key inducer for {110} twins could help us understand how crystal defects are controlled in biomineralization. In this study, we explore the role of a protein, twip1, in inducing a high density of {110} twins within the aragonite layers of the limpet shell. Through a combination of layer-specific protein profiling and in vitro aragonite binding assays, twip1 is identified as a potential protein preferentially binding to the aragonite (110) plane. Gene expression analysis via quantitative PCR (qPCR) confirmed that twip1 is specifically expressed in the mantle tissue. To further investigate its function, recombinant twip1 (rtwip1) is produced using an expression system. X-ray diffraction (XRD) and electron microscopy observations reveal that rtwip1 significantly increases {110} twin density during in vitro aragonite synthesis. Moreover, in vivo knockdown shows that reducing expression results in abnormal shell growth and {110} twin boundary reduction. Enhancing the formation of {110} twins in aragonite can improve its toughness and elasticity. This research highlights the crucial role of specific proteins in regulating crystal defect formation, offering a promising direction for future biomineralization studies and advanced material design.
文石是碳酸钙（CaCO）的一种多晶型物，由于存在诸如孪晶等晶体缺陷，其机械性能得到增强，这些缺陷在生物成因的文石中尤为普遍，并且能够抑制裂纹扩展。尽管其重要性，但海洋生物中负责文石{110}孪晶形成的分子机制仍知之甚少。确定{110}孪晶的关键诱导剂有助于我们理解生物矿化过程中晶体缺陷是如何被控制的。在本研究中，我们探究了一种蛋白质twip1在帽贝贝壳文石层内诱导高密度{110}孪晶的作用。通过结合层特异性蛋白质分析和体外文石结合试验，twip1被确定为一种潜在的优先结合文石（110）面的蛋白质。通过定量PCR（qPCR）进行的基因表达分析证实twip1在套膜组织中特异性表达。为了进一步研究其功能，使用表达系统产生了重组twip1（rtwip1）。X射线衍射（XRD）和电子显微镜观察表明，rtwip1在体外文石合成过程中显著增加{110}孪晶密度。此外，体内敲低显示表达降低会导致贝壳生长异常和{110}孪晶界减少。增强文石中{110}孪晶的形成可以提高其韧性和弹性。本研究突出了特定蛋白质在调节晶体缺陷形成中的关键作用，为未来的生物矿化研究和先进材料设计提供了一个有前景的方向。
