Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, WI 53706, USA.
Proc Natl Acad Sci U S A. 2012 Apr 17;109(16):6088-93. doi: 10.1073/pnas.1118085109. Epub 2012 Apr 4.
Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC · H(2)O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC · H(2)O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC · H(2)O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC · H(2)O in vitro.
结晶态生物矿物不同于具有明显晶面的晶体。目前对于这种特性的解释涉及无定形相形成过程。本文使用 X 射线吸收近边结构（XANES）光谱和光电子发射显微镜（PEEM），研究了紫海胆胚胎中骨针的形成过程，观察到三个矿物相的顺序：水合无定形碳酸钙（ACC·H₂O）→脱水无定形碳酸钙（ACC）→方解石。出人意料的是，我们发现了富含 ACC·H₂O 的纳米颗粒，在周围矿物脱水结晶后仍存在。嵌入在矿物中的蛋白质基质成分一定抑制了 ACC·H₂O 的脱水。我们设计了一种体外 XANES-PEEM 分析方法，以鉴定可能在稳定各种矿物相中起作用的骨针蛋白，发现最丰富的嵌在海胆骨针中的基质蛋白 SM50 在体外稳定 ACC·H₂O。
