Molecular Basis for the Hierarchical Dependency of Collagen Mechanics

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Type I collagen is the predominant collagen in mature tendons and ligaments, where it gives them their load-bearing mechanical properties. Fibrils of type I collagen are formed by the packing of polypeptide triple helices. Higher-order structures like fibril bundles and fibers are assembled from fibrils in the presence of other collagenous molecules and noncollagenous molecules. Experiments, including ours, show that the assembly of collagen molecules into fibrils/fibril-bundles makes them less resistant to axial stress — the Young's moduli of fibrils/fibril bundles are an order-of-magnitude smaller than the Young's moduli of triple helices. Here we will present results from our ongoing molecular dynamics studies (Proteins 83:1800-1812, 2015; Biophys J 111:50-56, 2016) that provide key insight into this hierarchical dependency. As such, these studies recommend a paradigm shift in our understanding of how collagen fibrils bear stress — we find that it is not the fibril core that bears the initial strain, as was thought, but it is the portion of the fibril exposed to the solvent and/or fibril-fibril interface that bear the initial strain. This has direct implication on understanding how various biological factors, including disease-causing congenital mutations and post-translational modifications, affect collagen structure, assembly and mechanics.

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Biophysical Journal, v. 114, issue 3, supp. 1, p. 59A