Molluscs, the largest marine phylum, display extraordinary shell diversity and sophisticated biomineral architectures. However, mineral-associated biomolecules involved in biomineralization are still poorly characterised. We report the first comprehensive structural and biomolecular study of Spondylus gaederopus, a pectinoid bivalve with a peculiar shell texture. Used since prehistoric times, this is the best-known shell of Europe's cultural heritage. We find that Spondylus microstructure is very poor in mineral-bound organics, which are mostly intercrystalline and concentrated at the interface between structural layers. Using high-resolution liquid chromatography tandem mass spectrometry (LC-MS/MS) we characterized several shell protein fractions, isolated following different bleaching treatments. Several peptides were identified as well as six shell proteins, which display features and domains typically found in biomineralized tissues, including the prevalence of intrinsically disordered regions. It is very likely that these sequences only partially represent the full proteome of Spondylus, considering the lack of genomics data for this genus and the fact that most of the reconstructed peptides do not match with any known shell proteins, representing consequently lineage-specific sequences. This work sheds light onto the shell matrix involved in the biomineralization in spondylids. Our proteomics data suggest that Spondylus has evolved a shell-forming toolkit, distinct from that of other better studied pectinoids - fine-tuned to produce shell structures with high mechanical properties, while limited in organic content. This study therefore represents an important milestone for future studies on biomineralized skeletons and provides the first reference dataset for forthcoming molecular studies of Spondylus archaeological artifacts.

中文翻译：

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欧洲多刺牡蛎的壳基质，Spondylus gaederopus：微观结构和分子特征。

软体动物是最大的海洋动物门，具有非凡的外壳多样性和复杂的生物矿物结构。然而，与生物矿化有关的矿物相关生物分子的特征仍然很差。我们报告了 Spondylus gaederopus 的第一次综合结构和生物分子研究，这是一种具有奇特壳质地的类果胶双壳类动物。自史前时代开始使用，这是欧洲文化遗产中最著名的外壳。我们发现 Spondylus 的微观结构在矿物结合有机物中非常差，这些有机物主要是晶间和集中在结构层之间的界面。使用高分辨率液相色谱串联质谱法 (LC-MS/MS)，我们表征了几种壳蛋白级分，在不同的漂白处理后分离。鉴定了几种肽以及六种壳蛋白，它们显示了生物矿化组织中常见的特征和结构域，包括固有无序区域的普遍性。考虑到缺乏该属的基因组学数据以及大多数重建的肽与任何已知的壳蛋白不匹配的事实，这些序列很可能仅部分代表了脊椎属的完整蛋白质组，因此代表了谱系特异性序列。这项工作揭示了参与脊椎生物矿化的壳基质。我们的蛋白质组学数据表明，Spondylus 已经进化出一种壳形成工具包，与其他更好研究的果胶不同——经过微调以产生具有高机械性能的壳结构，同时有机物含量有限。