Winter Benjamin, Butz Benjamin, Dieker Christel, Schröder-Turk Gerd E, Mecke Klaus, Spiecker Erdmann
Institute of Micro- and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy, Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany;
School of Engineering and Information Technology, Mathematics & Statistics, Murdoch University, Murdoch, 6150 WA, Australia;
Proc Natl Acad Sci U S A. 2015 Oct 20;112(42):12911-6. doi: 10.1073/pnas.1511354112. Epub 2015 Oct 5.
The wing scales of the Green Hairstreak butterfly Callophrys rubi consist of crystalline domains with sizes of a few micrometers, which exhibit a congenitally handed porous chitin microstructure identified as the chiral triply periodic single-gyroid structure. Here, the chirality and crystallographic texture of these domains are investigated by means of electron tomography. The tomograms unambiguously reveal the coexistence of the two enantiomeric forms of opposite handedness: the left- and right-handed gyroids. These two enantiomers appear with nonequal probabilities, implying that molecularly chiral constituents of the biological formation process presumably invoke a chiral symmetry break, resulting in a preferred enantiomeric form of the gyroid structure. Assuming validity of the formation model proposed by Ghiradella H (1989) J Morphol 202(1):69-88 and Saranathan V, et al. (2010) Proc Natl Acad Sci USA 107(26):11676-11681, where the two enantiomeric labyrinthine domains of the gyroid are connected to the extracellular and intra-SER spaces, our findings imply that the structural chirality of the single gyroid is, however, not caused by the molecular chirality of chitin. Furthermore, the wing scales are found to be highly textured, with a substantial fraction of domains exhibiting the <001> directions of the gyroid crystal aligned parallel to the scale surface normal. Both findings are needed to completely understand the photonic purpose of the single gyroid in gyroid-forming butterflies. More importantly, they show the level of control that morphogenesis exerts over secondary features of biological nanostructures, such as chirality or crystallographic texture, providing inspiration for biomimetic replication strategies for synthetic self-assembly mechanisms.
绿纹蛱蝶（Callophrys rubi）的翅鳞由尺寸为几微米的晶体域组成，这些晶体域呈现出一种先天性的手性多孔几丁质微观结构，被确定为手性三重周期单螺旋结构。在此，通过电子断层扫描研究了这些域的手性和晶体学织构。断层扫描清晰地揭示了两种相反手性的对映体形式共存：左旋和右旋螺旋体。这两种对映体出现的概率不相等，这意味着生物形成过程中分子手性成分可能引发了手性对称性破缺，从而导致螺旋体结构存在一种优先的对映体形式。假设吉拉代拉·H（1989年，《形态学杂志》202(1):69 - 88）以及萨兰纳坦·V等人（2010年，《美国国家科学院院刊》107(26):11676 - 11681）提出的形成模型有效，即螺旋体的两个对映体迷宫域与细胞外和内质网空间相连，然而我们的研究结果表明，单螺旋体的结构手性并非由几丁质的分子手性引起。此外，发现翅鳞具有高度的织构，相当一部分域的螺旋体晶体的<001>方向与鳞片表面法线平行排列。这两个发现对于全面理解形成螺旋体的蝴蝶中单个螺旋体的光子学目的都是必要的。更重要的是，它们展示了形态发生对生物纳米结构二级特征（如手性或晶体学织构）的控制水平，为合成自组装机制的仿生复制策略提供了灵感。
