Possible transient liquid crystal phase during the laying out of connective tissues:: α-chitin and collagen as models
Possible transient liquid crystal phase during the laying out of connective tissues:: α-chitin and collagen as models
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DOI：
10.1088/0953-8984/18/13/s08
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发表时间：
2006-04-05
影响因子：
2.7
通讯作者：
Giraud-Guille, M. M.
中科院分区：
文献类型：
--
作者：
Belamie, E.;Mosser, G.;Giraud-Guille, M. M.
细胞外基质的形态发生可以从不同的角度来考虑。一个是个体发生，即，生物体的发育，主要涉及基因的时空调控、细胞分化和迁移。作为对这种纯生物学观点的补充，物理化学方法可以通过突出不需要直接细胞控制的特定事件来帮助理解复杂的机制。由于某些生物系统和液晶之间的结构相似性，人们认为可能涉及类似的机制。在这方面，重要的是确定驱动生物大分子有序化的内在自组装特性。在这里，我们回顾了在体外研究的凝聚态的主要生物大分子从细胞外基质和相关的理论描述的中间相转变悬浮液中的棒状颗粒。胶原蛋白或几丁质的稀释悬浮液是各向同性的，即，大分子可以在流体中采取任何取向。超过一个临界浓度，出现一个有序的双相，具有较高的体积分数。在交叉偏振器之间可以看到两相共存，因为双折射相是强双折射的并且看起来很亮，而各向同性相保持黑暗。这些结构大分子支架的普遍性质是它们的手性。虽然胶体悬浮液中手性的起源仍然是一个争论的主题，但螺旋相的螺旋性质可以量化。在剪切对齐的样品上进行的小角度X射线散射可以帮助证明从光学观察推断的各向异性相的非线性性质。液体状的位置局部秩序揭示了在低角度的宽干涉峰的存在。这些图案的方位角的配置文件进行拟合，以确定的值的过渡处的有序参数。一些物理化学实验可以评估这种转变的性质，反过来，应用理论模型可以证明在预测和控制生物大分子组装体的结构方面是有用的。
Morphogenesis of extracellular matrices can be considered from different perspectives. One is that of ontogenesis, i.e., an organism's development, which is mostly concerned with the spatiotemporal regulation of genes, cell differentiation and migration. Complementary to this purely biological point of view, a physico-chemical approach can help in understanding complex mechanisms by highlighting specific events that do not require direct cellular control. Because of a structural similarity between some biological systems and liquid crystals, it was supposed that similar mechanisms could be involved. In this respect, it is important to determine the intrinsic self-assembly properties driving the ordering of biological macromolecules. Here we review in vitro studies of the condensed state of major biological macromolecules from extracellular matrices and related theories describing a mesophase transition in suspensions of rodlike particles. Dilute suspensions of collagen or chitin are isotropic, i.e., the macromolecules can take on any orientation in the fluid. Beyond a critical concentration, an ordered nematic phase appears with a higher volume fraction. The two-phase coexistence can be seen between crossed polarizers since the nematic phase is strongly birefringent and appears bright, whereas the isotropic phase remains dark. A widespread property of these structural macromolecular scaffolds is their chirality. Although the origin of chirality in colloidal suspensions is still a subject of debate, the helical nature of the cholesteric phase can be quantified. Small angle x-ray scattering performed on shear-aligned samples can help demonstrate the cholesteric nature of the anisotropic phase, inferred from optical observations. Liquid-like positional local order is revealed by the presence of broad interference peaks at low angle. The azimuthal profiles of these patterns are fitted to determine the value of the nematic order parameter at the transition. A few physico-chemistry experiments can assess the nature of the transition, and in turn, applying theoretical models can prove useful in predicting and controlling the structure of assemblies of biological macromolecules.