Weiss Ingrid M, Kaufmann Stefan, Heiland Birgit, Tanaka Motomu
INM-Leibniz Institute for New Materials gGmbH, Biomineralisation, Campus D2-2, 66123 Saarbrücken, Germany.
J Struct Biol. 2009 Jul;167(1):68-75. doi: 10.1016/j.jsb.2009.04.005. Epub 2009 May 4.
Molluscs have a well-deserved reputation for being expert mineralizers of various shell types such as nacre. Nacre is defined as regularly arranged layers and stacks of approximately 0.5 microm thick aragonite platelets that are extracellularly formed within a complex mixture of organic matrix. The control of species-specific layer thickness by the animal is still enigmatic. Despite the recent findings on the periodic layer-by-layer structures of chitin layers and silk-like protein layers in nacre-type biominerals, little is known about how the interface is defined between two different layers. In this paper, we demonstrate the presence of covalently attached, hydrophobic amino acid side chains in the chitin matrix in the bivalve mollusc Mytilus galloprovincialis by the combination of infrared spectroscopy and mass spectroscopy. The accumulation of the modified chitin matrix at the interface is quantified by the critical aggregate concentration of the purified chitin matrix, which is approximately an order of magnitude smaller than that of pure chitin. Our finding suggests an active role of such chemically modified chito-oligosaccharides in the creation of a defined interface and guidance of the periodic matrix textures, which would result in unique material properties of natural mollusc shells.
软体动物在形成各种贝壳类型（如珍珠质）方面堪称矿物化专家，这一美誉当之无愧。珍珠质被定义为由大约0.5微米厚的文石片晶规则排列而成的层和堆叠结构，这些文石片晶在有机基质的复杂混合物中细胞外形成。动物对物种特异性层厚度的控制仍然是个谜。尽管最近在珍珠质型生物矿物中发现了几丁质层和丝状蛋白质层的周期性逐层结构，但对于两个不同层之间的界面是如何界定的却知之甚少。在本文中，我们通过红外光谱和质谱联用，证明了在双壳类软体动物地中海贻贝的几丁质基质中存在共价连接的疏水氨基酸侧链。通过纯化几丁质基质的临界聚集浓度对界面处修饰几丁质基质的积累进行了量化，该浓度比纯几丁质的临界聚集浓度小约一个数量级。我们的发现表明，这种化学修饰的壳寡糖在形成明确的界面和引导周期性基质纹理方面发挥了积极作用，这将导致天然软体动物贝壳具有独特的材料特性。
