Extracellular matrix mechanics influence diverse cellular functions, yet surprisingly little is known about the mechanical properties of their constituent collagen proteins. In particular, network-forming collagen IV, an integral component of basement membranes, has been far less studied than fibril-forming collagens. A key feature of collagen IV is the presence of interruptions in the triple-helix-defining (Gly-X-Y) sequence along its collagenous domain. Here, we used atomic force microscopy to determine the impact of sequence heterogeneity on the local flexibility of collagen IV and of the fibril-forming collagen III. Our extracted flexibility profile of collagen IV reveals that it possesses highly heterogeneous mechanics, ranging from semiflexible regions as found for fibril-forming collagens to a lengthy region of high flexibility toward its N-terminus. A simple model in which flexibility is dictated only by the presence of interruptions fit the extracted profile reasonably well, providing insight into the alignment of chains and demonstrating that interruptions, particularly when coinciding in multiple chains, significantly enhance local flexibility. To a lesser extent, sequence variations within the triple helix lead to variable flexibility, as seen along the continuously triple-helical collagen III. We found this fibril-forming collagen to possess a high-flexibility region around its matrix-metalloprotease binding site, suggesting a unique mechanical fingerprint of this region that is key for matrix remodeling. Surprisingly, proline content did not correlate with local flexibility in either collagen type. We also found that physiologically relevant changes in pH and chloride concentration did not alter the flexibility of collagen IV, indicating such environmental changes are unlikely to control its compaction during secretion. Although extracellular chloride ions play a role in triggering collagen IV network formation, they do not appear to modulate the structure of its collagenous domain.

细胞外基质力学影响多种细胞功能，但令人惊讶的是，对其组成胶原蛋白的机械性能知之甚少。特别是，形成网络的胶原蛋白 IV 是基底膜的一个组成部分，其研究远远少于形成原纤维的胶原蛋白。胶原蛋白 IV 的一个关键特征是沿其胶原结构域的三螺旋定义 (Gly-XY) 序列存在中断。在这里，我们使用原子力显微镜来确定序列异质性对胶原蛋白 IV 和原纤维形成胶原蛋白 III 的局部柔韧性的影响。我们提取的胶原蛋白 IV 的柔韧性曲线表明它具有高度异质的力学，从形成原纤维的胶原蛋白的半柔性区域到朝向其 N 端的高柔性区域。一个简单的模型，其中仅由中断的存在决定了灵活性，与提取的轮廓相当吻合，提供了对链对齐的洞察力，并证明了中断，特别是在多个链中重合时，显着提高了局部灵活性。在较小程度上，三螺旋内的序列变化导致可变的灵活性，如沿连续三螺旋胶原 III 所见。我们发现这种形成原纤维的胶原蛋白在其基质-金属蛋白酶结合位点周围具有高柔韧性区域，这表明该区域具有独特的机械指纹，这是基质重塑的关键。出奇，脯氨酸含量与两种胶原蛋白类型的局部柔韧性无关。我们还发现，pH 和氯化物浓度的生理相关变化并没有改变胶原蛋白 IV 的柔韧性，这表明这种环境变化不太可能控制其分泌过程中的压实。尽管细胞外氯离子在触发胶原蛋白 IV 网络形成中起作用，但它们似乎不会调节其胶原结构域的结构。