Laminin polymerization is a key step of basement membrane assembly that depends on the binding of α, β and γ N-terminal LN domains to form a polymer node. Nodal assembly can be divided into two steps consisting of β- and γ-LN dimerization followed by calcium-dependent addition of the α-LN domain. The assembly and structural organization of laminin-111 LN-LEa segments was examined by size-exclusion chromatography (SEC) and electron microscopy. Triskelion-like structures were observed in negatively-stained images of purified α1/β1/γ1 LN-LEa trimers. Image averaging of these revealed a heel-to-toe organization of the LN domains with angled outward projections of the LEa stem-like domains. A series of single-amino acid substitutions was introduced into the polymerization faces of the α1, β1 and γ1 LN domains followed by SEC analysis to distinguish between loss of β-γ mediated dimerization and loss of α-dependent trimerization (with intact β-γ dimers). Dimer-blocking mutations were confined to the γ1-toe and the β1-heel, whereas the trimer-only-blocking mutations mapped to the γ1-heel, β1-toe and the α1-toe and heel. Thus, in the polymer node the γ1-toe pairs with the β1-heel, the β1-toe pairs with the α1-heel, and the α1-toe pairs with the γ1-heel.

层粘连蛋白聚合是基底膜组装的关键步骤，它依赖于 α、β 和 γ N 端 LN 结构域的结合形成聚合物节点。节点组装可以分为两个步骤，包括 β-和 γ-LN 二聚化，然后是钙依赖性添加 α-LN 结构域。层粘连蛋白 111 LN-LEa 片段的组装和结构组织通过尺寸排阻色谱 (SEC) 和电子显微镜检查。在纯化的 α1/β1/γ1 LN-LEa 三聚体的负染色图像中观察到 Triskelion 样结构。这些图像的平均显示了 LN 域的从脚跟到脚趾的组织，具有 LEa 茎状域的有角度的向外投影。在 α1 的聚合面上引入了一系列单氨基酸取代，β1 和 γ1 LN 结构域，然后进行 SEC 分析，以区分 β-γ 介导的二聚体的丧失和 α 依赖性三聚体的丧失（具有完整的 β-γ 二聚体）。二聚体阻断突变仅限于 γ1-toe 和 β1-heel，而仅三聚体阻断突变映射到 γ1-heel、β1-toe 和 α1-toe 和鞋跟。因此，在聚合物节点中，γ1 趾对与β1 鞋跟，β1 趾对与α1 鞋跟，α1 趾对与γ1 鞋跟。