Pasquali-Ronchetti I, Fornieri C, Baccarani-Contri M, Quaglino D
Ciba Found Symp. 1995;192:31-42; discussion 42-50.
Almost all structural studies on elastin have been done in higher vertebrates, in which it is organized as an extracellular network of branched fibres which vary from fractions f microns to several microns in diameter. By conventional electron microscopy, elastin appears amorphous. By both freeze-fracture and negative staining on cryosections, it can be resolved as beaded filaments 5 nm in diameter forming a 3D meshwork that, upon stretching, becomes oriented in the direction of the force applied. This filamentous aggregation of elastin molecules is confirmed in vitro by the observation that its soluble precursor, tropoelastin, shows a strong tendency to associate into short 5 nm-thick filaments that, with time, become longer and aggregate into bundles of various dimensions. If chemically fixed and embedded, these aggregates appear amorphous and identical to natural elastin fibres. The tendency of tropoelastin to aggregate into 4-5 nm-thick beaded filaments, which then associate into 12 nm-thick filaments forming a 3D network, has been observed by atomic force microscopy for recombinant human tropoelastin. Therefore, the amorphous structure of elastin seems to be a technical artefact. Apart from elastin-associated microfibrils, which are always present at the periphery of growing elastic fibres and probably have a role more complex than being a scaffold for tropoelastin aggregation in vivo, the elastic fibres seem to be composed of several matrix constituents, which are different in different organs and change with age and in pathological conditions. This is demonstrated by immunocytochemical studies on ultrathin sections.
几乎所有关于弹性蛋白的结构研究都是在高等脊椎动物中进行的，在这些动物中，弹性蛋白组织成细胞外分支纤维网络，其直径从几微米到几微米不等。通过传统电子显微镜观察，弹性蛋白呈现无定形。通过冷冻断裂和对冷冻切片进行负染色，可将其解析为直径5纳米的串珠状细丝，形成三维网络，拉伸时会沿施加力的方向排列。弹性蛋白分子的这种丝状聚集在体外得到证实，因为观察发现其可溶性前体原弹性蛋白有强烈的倾向聚合成短的5纳米厚的细丝，随着时间推移，这些细丝会变得更长并聚集成各种尺寸的束。如果进行化学固定和包埋，这些聚集体看起来无定形，与天然弹性纤维相同。通过原子力显微镜对重组人原弹性蛋白的观察，发现原弹性蛋白有聚合成4 - 5纳米厚的串珠状细丝的倾向，然后这些细丝会结合成12纳米厚的细丝，形成三维网络。因此，弹性蛋白的无定形结构似乎是一种技术假象。除了与弹性蛋白相关的微原纤维，它们总是存在于生长中的弹性纤维外围，其作用可能比在体内作为原弹性蛋白聚集的支架更为复杂，弹性纤维似乎由几种基质成分组成，不同器官中的这些成分不同，且会随年龄和病理状况而变化。这在超薄切片的免疫细胞化学研究中得到了证明。
