Understanding polymorph production and control in calcite/aragonite biominerals

了解方解石/文石生物矿物中多晶型物的产生和控制

• 批准号: BB/E025110/1
• 负责人: Andrew A. Freer
• 金额: $ 42.19万
• 依托单位: University of Glasgow
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FE025110%2F1
• 关键词: Understanding; polymorph; production; control; calcite

As children we all looked forward to our beach holidays, playing in the sand, building castles. These ephemeral structures we would often decorate with shells gathered from the foreshore. Sometimes luck prevailed and we found opened shells but more than likely we would scavenge and find mussels attached to nearby rocks. In Scottish waters these were more than likely the common blue mussel, Mytilus edulis, which, should we try and open them or smash them with a rock, we would find quite resilient, tough. This resilience is due to the unique shell structure laid down by the mollusc as it grows. How it does this is by recruiting certain proteins, unique to molluscs, to convert the basic shell material, calcium carbonate, into ordered layered structures. If you look at the external surface of the mussel it is rough and with a bit of effort you may be able to dislodge some of the surface coat. However, if you look at the inside of the shell there is a pearlescent material, called nacre, which is many times tougher than the outer coat. By cutting the shell in a specific direction and using an electron microscope to look in great detail at the arrangement of this calcium carbonate we find two forms (called polymorphs) - calcite on the outer layer and aragonite in the inner (nacre) layer. Although calcite readily forms from calcium carbonate in the laboratory, aragonite is a high-pressure polymorph which, as the name suggests, requires high pressure for the tougher form to be produced. A good analogy is that aragonite is to calcite as diamond is to graphite / both materials are made from the same chemical elements, but have quite different characteristics. The purpose of this project is to determine how the humble sea mollusc produces calcite and aragonite at ambient temperature and pressure, a feat that is not possible under normal laboratory conditions. To do this we have to examine both the shell architecture and also the proteins that may be recruited to accomplish this production of calcite and aragonite. The shell architecture will be looked at in fine detail by using two techniques / scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD). This will allow us to see this arrangement of calcite and aragonite within the shell. Simultaneously, we will look at a number of proteins that are found in the extrapallial (EP) fluid / which is found between the nacre layer and the soft (edible) part of the mussel and is easily extracted with a syringe. This EP fluid, which contains a number of different proteins, is thought to be the source of proteins needed to carry out the transformation from calcite to aragonite. In this project, several of these individual proteins will be isolated from the EP fluid and used to determine exactly which ones influence this change from calcite to aragonite. SEM and EBSD will be used to follow the growth of calcite/aragonite in a laboratory environment and hence we can determine which proteins cause the switch. Within the EP fluid there is one protein that stands out more than all the others and we will investigate this protein first since this is the most likely candidate for transformation. The most exciting way to do this is to determine its 3-D structure by using X-ray diffraction, a technique that the protein group in Glasgow excels. By knowing the structure we can determine how it works. So, what good is all this? Well, two important aspects: firstly, if you can control this switching you can sequentially lay down different layers on a number of different substrates (which we will also investigate). There is evidence that the aragonite nacre could potentially be exploited in the stimulation of bone production in osteoporosis for example if synthetic nacre could be provided in a suitable form. Secondly, the physical characteristics (extreme hardness) of aragonite nacre could also be exploited in a number of ways / protection for fragile surfaces and humans.

小时候，我们都盼望着海滩假期，在沙滩上玩耍，建造城堡。我们经常用从前滨采集的贝壳来装饰这些短暂的结构。有时运气占了上风，我们发现了打开的贝壳，但更有可能的是，我们会发现贻贝附着在附近的岩石上。在苏格兰的沃茨，这些很可能是常见的蓝色贻贝，紫贻贝，如果我们试图打开它们，或者用石头砸碎它们，我们会发现它们非常有弹性，坚韧。这种弹性是由于软体动物在生长过程中形成的独特外壳结构。它是如何做到这一点的是通过招募某些蛋白质，独特的软体动物，以转换基本的外壳材料，碳酸钙，到有序的层状结构。如果你看贻贝的外表面，它很粗糙，只要稍微努力，你就可以去除一些表面涂层。然而，如果你看一下贝壳的内部，有一种珠光材料，称为珍珠层，它比外壳坚硬许多倍。通过在一个特定的方向切割贝壳，并使用电子显微镜来观察这种碳酸钙的排列细节，我们发现了两种形式（称为多晶型物）-外层的方解石和内层（珍珠层）的文石。虽然方解石在实验室中很容易由碳酸钙形成，但文石是一种高压多晶型物，顾名思义，需要高压才能产生更坚硬的形式。一个很好的类比是，文石与方解石的关系就像金刚石与石墨的关系一样，这两种材料都是由相同的化学元素制成的，但具有完全不同的特性。该项目的目的是确定这种不起眼的海洋软体动物如何在环境温度和压力下产生方解石和文石，这是在正常实验室条件下不可能实现的壮举。要做到这一点，我们必须检查两个壳结构，也可以招募完成方解石和文石的生产蛋白质。壳结构将通过使用两种技术/扫描电子显微镜（SEM）和电子背散射衍射（EBSD）来详细观察。这将使我们看到这种安排的方解石和文石在壳。同时，我们将研究一些蛋白质，这些蛋白质存在于珍珠层和贻贝柔软（可食用）部分之间的外膜（EP）液中，并且很容易用注射器提取。这种EP流体含有许多不同的蛋白质，被认为是进行从方解石到文石的转化所需的蛋白质的来源。在这个项目中，将从EP流体中分离出这些单独的蛋白质中的几种，并用于确定哪些蛋白质会影响方解石到文石的变化。SEM和EBSD将用于跟踪实验室环境中方解石/文石的生长，因此我们可以确定哪些蛋白质导致了这种转变。在EP液体中，有一种蛋白质比所有其他蛋白质更突出，我们将首先研究这种蛋白质，因为这是最有可能进行转化的候选蛋白质。最令人兴奋的方法是使用X射线衍射确定其三维结构，格拉斯哥的蛋白质组擅长这项技术。通过了解结构，我们可以确定它如何工作。所以，这有什么用？那么两个重要的方面：首先，如果你能控制这种转换，你就能在许多不同的衬底上顺序地放置不同的层（我们也将研究）。有证据表明，文石珍珠层可以潜在地用于刺激骨质疏松症中的骨生成，例如，如果可以以合适的形式提供合成珍珠层。其次，文石珍珠层的物理特性（极高的硬度）也可以以多种方式利用/保护脆弱的表面和人类。

项目成果

Biomineral shell formation under ocean acidification: a shift from order to chaos.

• DOI: 10.1038/srep21076
• 发表时间: 2016-02-15
• 期刊: Scientific reports
• 影响因子: 4.6
• 作者: Fitzer SC;Chung P;Maccherozzi F;Dhesi SS;Kamenos NA;Phoenix VR;Cusack M
• 通讯作者: Cusack M

Oxygen isotope composition in Modiolus modiolus aragonite in the context of biological and crystallographic control

生物和晶体学控制背景下Modiolus modiolus文石中的氧同位素组成

• DOI: 10.1180/minmag.2008.072.2.569
• 发表时间: 2018
• 期刊: Mineralogical Magazine
• 影响因子: 2.7
• 作者: Cusack M

Shell proteome of rhynchonelliform brachiopods.

• DOI: 10.1016/j.jsb.2015.04.001
• 发表时间: 2015-06
• 期刊: Journal of structural biology
• 影响因子: 3
• 作者: F. Immel;D. Gaspard;A. Marie;N. Guichard;M. Cusack;F. Marin

Ocean acidification and temperature increase impact mussel shell shape and thickness: problematic for protection?

• DOI: 10.1002/ece3.1756
• 发表时间: 2015-11
• 期刊: Ecology and evolution
• 影响因子: 2.6
• 作者: Fitzer SC;Vittert L;Bowman A;Kamenos NA;Phoenix VR;Cusack M
• 通讯作者: Cusack M

Micro-XANES mapping of sulphur and its association with magnesium and phosphorus in the shell of the brachiopod, Terebratulina retusa

腕足动物壳中硫及其与镁和磷的关联的 Micro-XANES 绘图

• DOI: 10.1016/j.chemgeo.2008.05.007
• 发表时间: 2008
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Cusack M