Faculty of Dentistry, McGill University, Montreal, QC, Canada.
J Struct Biol. 2010 Apr;170(1):50-9. doi: 10.1016/j.jsb.2010.01.009. Epub 2010 Jan 28.
Fibronectin (FN) is an extracellular glycoprotein with critical roles in many fundamental biological processes. A hallmark of FN function is its characteristic assembly into filaments and fibers to form an insoluble matrix which functions as a scaffolding onto which cells attach, migrate, and deposit other matrix constituents. In this study, we have investigated the effects of differently charged and functionalized surfaces on FN conformations using atomic force microscopy. We demonstrate that a negatively charged polysulfonated surface promotes the formation of highly periodic, micrometer-long FN filaments having a "bead-on-a-string" structure with a bead periodicity of about 60 nm. Beaded filaments were observed when FN was adsorbed to polysulfonate surface in water; higher ionic strength allowed formation of filamentous structures but altered the regularity of the beads. FN did not form filaments when adsorbed onto the polysulfonate surface in the presence of soluble polysulfonates emphasizing the role of negatively charged, solid-phase elements on FN assembly. This charge-driven assembly likely derives from the negative surface promoting extension and opening of the protein, and we suggest a model where this assembly pattern is further stabilized by known self-assembly regions. Our results give insight into how FN fibrillogenesis might be promoted in vivo at cell surfaces by the negatively charged and sulfonated environment created by cell-surface, transmembrane proteoglycans.
纤连蛋白（FN）是一种细胞外糖蛋白，在许多基本的生物学过程中具有关键作用。FN 功能的一个显著特点是其特征性地组装成纤维和纤维，形成不溶性基质，作为细胞附着、迁移和沉积其他基质成分的支架。在这项研究中，我们使用原子力显微镜研究了不同带电和功能化表面对 FN 构象的影响。我们证明，带负电荷的多磺化表面促进了高度周期性的、长达微米的 FN 纤维的形成，这些纤维具有“珠串”结构，珠的周期性约为 60nm。当 FN 在水中吸附到多磺酸盐表面时，会观察到珠状纤维；较高的离子强度允许形成丝状结构，但改变了珠子的规则性。当 FN 在存在可溶性多磺酸盐的情况下吸附到多磺酸盐表面时，不会形成纤维，这强调了带负电荷的固相元素对 FN 组装的作用。这种电荷驱动的组装可能源于负表面促进蛋白质的延伸和展开，我们提出了一个模型，其中这种组装模式进一步由已知的自组装区域稳定。我们的研究结果深入了解了细胞表面的跨膜蛋白聚糖所产生的带负电荷和磺化环境如何在体内促进 FN 的纤维形成。
