Collagens are the foundational component of diverse tissues, including skin, bone, cartilage, and basement membranes, and are the most abundant protein class in animals. The fibrillar collagens are large, complex, multidomain proteins, all containing the characteristic triple helix motif. The most prevalent collagens are heterotrimeric, meaning that cells express at least two distinctive procollagen polypeptides that must assemble into specific heterotrimer compositions. The molecular mechanisms ensuring correct heterotrimeric assemblies are poorly understood – even for the most common collagen, type-I. The longstanding paradigm is that assembly is controlled entirely by the ~30 kDa globular C-propeptide (C-Pro) domain. Still, this dominating model for procollagen assembly has left many questions unanswered. Here, we show that the C-Pro paradigm is incomplete. In addition to the critical role of the C-Pro domain in templating assembly, we find that the amino acid sequence near the C terminus of procollagen’s triple-helical domain plays an essential role in defining procollagen assembly outcomes. These sequences near the C terminus of the triple-helical domain encode conformationally stabilizing features that ensure only desirable C-Pro-mediated trimeric templates are committed to irreversible triple-helix folding. Incorrect C-Pro trimer assemblies avoid commitment to triple-helix formation thanks to destabilizing features in the amino acid sequences of their triple helix. Incorrect C-Pro assemblies are consequently able to dissociate and search for new binding partners. These findings provide a distinctive perspective on the mechanism of procollagen assembly, revealing the molecular basis by which incorrect homotrimer assemblies are avoided and setting the stage for a deeper understanding of the biogenesis of this ubiquitous protein.

中文翻译：

---

三螺旋结构域在调节胶原蛋白 I 组装中的结局决定作用


胶原蛋白是多种组织的基础成分，包括皮肤、骨骼、软骨和基底膜，是动物中最丰富的蛋白质类别。纤维状胶原蛋白是大型、复杂的、多结构域的蛋白质，均包含特征性的三螺旋基序。最普遍的胶原蛋白是异源三聚体，这意味着细胞表达至少两种独特的前胶原多肽，这些多肽必须组装成特定的异源三聚体组合物。确保正确异源三聚体组装体的分子机制知之甚少——即使对于最常见的胶原蛋白 I 型也是如此。长期以来的范式是组装完全由 ~30 kDa 球状 C-前肽 （C-Pro） 结构域控制。尽管如此，这种前胶原组装的主导模型仍有许多问题没有得到解答。在这里，我们表明 C-Pro 范例是不完整的。除了 C-Pro 结构域在模板组装中的关键作用外，我们还发现前胶原三螺旋结构域 C 末端附近的氨基酸序列在定义前胶原组装结果中起着至关重要的作用。这些序列靠近三螺旋结构域的 C 末端编码构象稳定特征，确保只有理想的 C-Pro 介导的三聚体模板才能进行不可逆的三螺旋折叠。不正确的 C-Pro 三聚体组装体由于其三螺旋氨基酸序列中的不稳定特征而避免了三螺旋形成。因此，不正确的 C-Pro 组件能够解离并寻找新的结合伴侣。 这些发现为前胶原组装的机制提供了独特的视角，揭示了避免不正确的同源三聚体组装的分子基础，并为更深入地了解这种普遍存在的蛋白质的生物发生奠定了基础。