Sone Eli D, Weiner Steve, Addadi Lia
Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel.
J Struct Biol. 2007 Jun;158(3):428-44. doi: 10.1016/j.jsb.2007.01.001. Epub 2007 Jan 8.
The continuously growing limpet radula contains teeth at various stages of maturity and thus provides an excellent opportunity for studying the processes and mechanisms of their mineralization. We report here on our structural investigations of the pre-formed chitin matrix and the initial deposition and growth of goethite (alpha-FeOOH) crystals within the matrix. By using cryo-techniques, in which unstained sections of the teeth are examined in a frozen-hydrated state in a transmission electron microscope (TEM), we were able to characterize the process without introducing artifacts normally associated with the staining, dehydration, and embedding required for conventional TEM. The unmineralized matrix consists of relatively well ordered, densely packed arrays of chitin fibers, with only a few nanometers between adjacent fibers. There are clearly no pre-formed compartments that control goethite crystal size and shape; rather, crystals must push aside or engulf the fibers as they grow. By examining teeth nearly row-by-row around the onset of mineralization, we were able to image the first-formed mineral within the chitin matrix. These linear deposits of goethite appear to nucleate on the chitin fibers, which thus control the orientation of the crystals. Crystal growth, on the other hand, is apparently not influenced by the matrix, in contrast to many other biomineralization systems.
不断生长的帽贝齿舌包含处于不同成熟阶段的齿，因此为研究其矿化过程和机制提供了绝佳机会。我们在此报告对预先形成的几丁质基质以及基质中针铁矿（α-FeOOH）晶体的初始沉积和生长的结构研究。通过使用低温技术，即在透射电子显微镜（TEM）中以冷冻水合状态检查未染色的齿切片，我们能够表征该过程，而不会引入通常与传统TEM所需的染色、脱水和包埋相关的假象。未矿化的基质由排列相对有序、紧密堆积的几丁质纤维阵列组成，相邻纤维之间只有几纳米。显然没有预先形成的隔室来控制针铁矿晶体的大小和形状；相反，晶体在生长时必须推开或吞噬纤维。通过在矿化开始时几乎逐行检查齿，我们能够对几丁质基质中最初形成矿物进行成像。这些针铁矿的线性沉积物似乎在几丁质纤维上成核，从而控制晶体的取向。另一方面，与许多其他生物矿化系统不同，晶体生长显然不受基质的影响。
