Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611-6400, USA.
Colloids Surf B Biointerfaces. 2013 Dec 1;112:42-50. doi: 10.1016/j.colsurfb.2013.07.037. Epub 2013 Jul 26.
Even though the behavior of collagen monomers self-assembling into fibrils is commonly understood in terms of hydrophobic and electrostatic interactions, the mechanisms that drive their ordered, longitudinal alignment to form a characteristic periodicity are still unclear. By introducing various salts into the collagen fibrillogenesis system, the intermolecular interactions of fibril formation were studied. We found that the pH and ion species play a critical role in forming native fibrils. Turbidity and electron microscopy revealed that collagen self-assembled into fibrils with a native banding pattern in the presence of multivalent ions. The isoelectric point of collagen in 12mM of NaCl is pH 8.9; it shifted to pH 9.4 and pH 7.0 after adding 10mM CaCl2 and Na2SO4, respectively. Native fibrils were reconstituted at pH 7.4 in salts with divalent anions and at pH 9.0 in salts with divalent cations. Circular dichroism spectroscopy showed a loss of helicity in the conditions where fibrillogenesis was unable to be achieved. The multivalent ions not only change the surface charge of collagen, but also facilitate the formation of fibrils with the native D-periodic banding pattern. It is likely that the binding multivalent ions induce the like-charge attraction and facilitate monomers' longitudinal registration to form fibrils with the native banding.
尽管胶原单体自组装成原纤维的行为通常可以用疏水相互作用和静电相互作用来解释，但驱动其有序的、纵向排列以形成特征周期性的机制仍不清楚。通过在胶原纤维原形成系统中引入各种盐，研究了纤维形成的分子间相互作用。我们发现 pH 值和离子种类在形成天然纤维方面起着关键作用。浊度和电子显微镜显示，在多价离子存在的情况下，胶原自组装成具有天然带纹图案的纤维。在 12mM NaCl 中胶原的等电点为 pH8.9；分别加入 10mM CaCl2 和 Na2SO4 后，其等电点分别移至 pH9.4 和 pH7.0。在带二价阴离子的盐中于 pH7.4 以及在带二价阳离子的盐中于 pH9.0 可重新形成天然纤维。圆二色性光谱显示，在无法实现纤维原形成的条件下，螺旋性丧失。多价离子不仅改变了胶原的表面电荷，而且还促进了具有天然 D 周期带纹图案的纤维的形成。很可能是结合的多价离子诱导了同电荷吸引，并促进了单体的纵向注册，形成具有天然带纹的纤维。
