Gale M, Pollanen M S, Markiewicz P, Goh M C
Department of Chemistry, University of Toronto, Ontario, Canada.
Biophys J. 1995 May;68(5):2124-8. doi: 10.1016/S0006-3495(95)80393-0.
Most polymers which comprise biological filaments assemble by two mechanisms: nucleation and elongation or a sequential, stepwise process involving a hierarchy of intermediate species. We report the application of atomic force microscopy (AFM) to the study of the early events in the sequential or stepwise mode of assembly of a macromolecular filament. Collagen monomers were assembled in vitro and the early structural intermediates of the assembly process were examined by AFM and correlated with turbidimetric alterations in the assembly mixture. The assembly of collagen involved a sequence of distinctive filamentous species which increased in both diameter and length over the time course of assembly. The first discrete population of collagen oligomers were 1-2 nm in diameter (300-500 nm in length); at later time points, filaments approximately 2-6 nm in diameter (> 10 microns in length) many with a conspicuous approximately 67-nm axial period were observed. Occasional mature collagen fibrils with a approximately 67-nm axial repeat were found late in the course of assembly. Our results are consistent with initial end-to-end axial association of monomers to form oligomers followed by lateral association into higher-order filaments. On this basis, there appears to be at least two distinctive types of structural interactions (axial and lateral) which are operative at different levels in the assembly hierarchy of collagen.
成核和伸长，或者是一个涉及一系列中间物种的连续、逐步过程。我们报道了原子力显微镜（AFM）在研究大分子细丝连续或逐步组装模式早期事件中的应用。胶原蛋白单体在体外组装，组装过程的早期结构中间体通过AFM进行检测，并与组装混合物中的比浊变化相关联。胶原蛋白的组装涉及一系列独特的丝状物种，它们在组装过程中直径和长度都增加。第一批离散的胶原蛋白低聚物直径为1 - 2纳米（长度为300 - 500纳米）；在稍后的时间点，观察到直径约为2 - 6纳米（长度大于10微米）的细丝，许多细丝具有明显的约67纳米轴向周期。在组装过程后期偶尔会发现具有约67纳米轴向重复的成熟胶原纤维。我们的结果与单体最初端对端轴向缔合形成低聚物，随后横向缔合形成高阶细丝一致。在此基础上，似乎至少有两种独特类型的结构相互作用（轴向和横向）在胶原蛋白组装层次结构的不同水平上起作用。
