Corals are the ecosystem engineers of coral reefs, one of the most biodiverse marine ecosystems. The ability of corals to form reefs depends on the precipitation of calcium carbonate (CaCO₃) under biological control. However, several mechanisms underlying coral biomineralization remain elusive, e.g. whether corals employ different molecular machineries to deposit different CaCO₃ polymorphs (i.e., aragonite or calcite). Here we used tandem mass spectrometry (MS/MS) to compare the proteins occluded in the skeleton of three octocoral and one scleractinian species: Tubipora musica and Sinularia cf. cruciata (calcite sclerites), the blue coral Heliopora coerulea (aragonitic skeleton), and the scleractinian aragonitic Montipora digitata. Reciprocal Blast analysis revealed extremely low overlap between aragonitic and calcitic species, while a core set of proteins is shared between octocorals producing calcite sclerites. However, the carbonic anhydrase CruCA4 is present in the skeletons of both polymorphs. Phylogenetic analysis highlighted several possible instances of protein co-option in octocorals. These include acidic proteins and scleritin, which appear to have been secondarily recruited for calcification and likely derive from proteins playing different functions. Similarities between octocorals and scleractinians included presence of a galaxin-related protein, carbonic anhydrases and one hephaestin-like protein. While the first two appear to have been independently recruited, the third appear to share a common origin. This work represents the first attempt to identify and compare proteins associated with coral skeleton polymorph diversity, providing several new research targets and enabling both future functional and evolutionary studies aimed at elucidating the origin and evolution of coral biomineralization.

中文翻译：

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八眼和巩膜骨架的比较蛋白质组学和珊瑚钙化的演变。

珊瑚是生物多样性最丰富的海洋生态系统之一的珊瑚礁的生态系统工程师。珊瑚形成珊瑚礁的能力取决于在生物控制下碳酸钙（CaCO ₃）的沉淀。但是，珊瑚生物矿化的几种机制仍然难以捉摸，例如，珊瑚是否利用不同的分子机制沉积不同的CaCO ₃多晶型物（即文石或方解石）。在这里，我们使用串联质谱（MS / MS）来比较三种八叶虫和一种Scleractinian物种（Tubipora musica和Sinularia cf.）的骨架中所含的蛋白质。cruciata（方解石sclerites），蓝色珊瑚Heliopora coerulea（古猿骨架）和巩膜古生物蒙太奇digitata。相互冲击波分析显示，古生物和钙钙石物种之间的重叠极低，而八方珊瑚生产方解石硬钙石时共享一组核心蛋白质。但是，碳酸酐酶CruCA4存在于两种多晶型物的骨架中。系统发育分析突出了八齿鱼蛋白质共选的几种可能实例。这些包括酸性蛋白质和硬化蛋白，它们似乎已被第二次募集用于钙化，并且可能源自发挥不同功能的蛋白质。Octocorals和scleractinians之间的相似之处包括存在与盖拉辛相关的蛋白，碳酸酐酶和一种类肝素蛋白。前两个似乎是独立招募的，第三个似乎有共同的血统。