Molluscs are one of the most diversified phyla among metazoans. Most of them produce an external calcified shell, resulting from the secretory activity of a specialized epithelium of the calcifying mantle. This biomineralization process is controlled by a set of extracellular macromolecules, the organic matrix. In spite of several studies, these components are mainly known for bivalves and gastropods. In the present study, we investigated the physical and biochemical properties of the internal planispiral shell of the Ram's Horn squid Spirula spirula. Scanning Electron Microscope investigations of the shell reveal a complex microstructural organization. The saccharides constitute a quantitatively important moiety of the matrix, as shown by Fourier-transform infrared and solid-state nuclear magnetic resonance spectroscopies. NMR identified β-chitin and additional polysaccharides for a total amount of 80% of the insoluble fraction. Proteomics was applied to both soluble and insoluble matrices and in silico searches were performed, first on heterologous metazoans models, and secondly on an unpublished transcriptome of Spirula spirula. In the first case, several peptides were identified, some of them matching with tyrosinase, chitinase 2, protease inhibitor, or immunoglobulin. In the second case, 39 hits were obtained, including transferrin, a serine protease inhibitor, matrilin, or different histones. The very few similarities with known molluscan shell matrix proteins suggest that Spirula spirula uses a unique set of shell matrix proteins for constructing its internal shell. The absence of similarity with closely related cephalopods demonstrates that there is no obvious phylogenetic signal in the cephalopod skeletal matrix.

中文翻译：

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羊角鱿鱼的壳基质和微观结构：分子和结构表征。

软体动物是后生动物中最多样化的门之一。它们中的大多数产生外部钙化壳，这是由钙化地幔的特殊上皮的分泌活动产生的。这种生物矿化过程由一组细胞外大分子有机基质控制。尽管进行了多项研究，但这些成分主要以双壳类和腹足类动物为人所知。在本研究中，我们调查了公羊角鱿鱼 Spirula spirula 的内部平面螺旋壳的物理和生化特性。外壳的扫描电子显微镜研究揭示了一个复杂的微观结构组织。如傅立叶变换红外光谱和固态核磁共振光谱所示，糖类构成了基质的重要数量部分。NMR 鉴定了 80% 的不溶性部分的 β-几丁质和其他多糖。蛋白质组学应用于可溶性和不溶性基质，并进行了计算机搜索，首先是在异源后生动物模型上，其次是在未发表的螺旋藻转录组上。在第一种情况下，鉴定了几种肽，其中一些与酪氨酸酶、几丁质酶 2、蛋白酶抑制剂或免疫球蛋白相匹配。在第二种情况下，获得了 39 个命中，包括转铁蛋白、丝氨酸蛋白酶抑制剂、matrilin 或不同的组蛋白。与已知软体动物壳基质蛋白的极少相似之处表明螺旋藻使用一组独特的壳基质蛋白来构建其内壳。