Buehler Markus J, Wong Sophie Y
Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Biophys J. 2007 Jul 1;93(1):37-43. doi: 10.1529/biophysj.106.102616. Epub 2007 Apr 13.
We report molecular modeling of stretching single molecules of tropocollagen, the building block of collagen fibrils and fibers that provide mechanical support in connective tissues. For small deformation, we observe a dominance of entropic elasticity. At larger deformation, we find a transition to energetic elasticity, which is characterized by first stretching and breaking of hydrogen bonds, followed by deformation of covalent bonds in the protein backbone, eventually leading to molecular fracture. Our force-displacement curves at small forces show excellent quantitative agreement with optical tweezer experiments. Our model predicts a persistence length xi(p) approximately 16 nm, confirming experimental results suggesting that tropocollagen molecules are very flexible elastic entities. We demonstrate that assembly of single tropocollagen molecules into fibrils significantly decreases their bending flexibility, leading to decreased contributions of entropic effects during deformation. The molecular simulation results are used to develop a simple continuum model capable of describing an entire deformation range of tropocollagen molecules. Our molecular model is capable of describing different regimes of elastic and permanent deformation, without relying on empirical parameters, including a transition from entropic to energetic elasticity.
我们报道了原胶原蛋白单分子拉伸的分子模拟，原胶原蛋白是构成胶原纤维的基本单元，而胶原纤维在结缔组织中提供机械支撑。对于小变形，我们观察到熵弹性占主导。在较大变形时，我们发现向能弹性的转变，其特征是首先氢键拉伸和断裂，随后蛋白质主链中的共价键变形，最终导致分子断裂。我们在小力作用下的力 - 位移曲线与光镊实验显示出极好的定量一致性。我们的模型预测持久长度ξ(p)约为16纳米，证实了实验结果，即原胶原分子是非常灵活的弹性实体。我们证明单原胶原分子组装成纤维会显著降低其弯曲柔韧性，导致变形过程中熵效应的贡献减少。分子模拟结果用于开发一个简单的连续介质模型，该模型能够描述原胶原分子的整个变形范围。我们的分子模型能够描述弹性和永久变形的不同状态，而无需依赖经验参数，包括从熵弹性到能弹性的转变。
