First full atomistic model of collagen microfibril

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• published: 02 Aug 2011
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Collagen is the most abundant protein in humans, providing mechanical stability, elasticity, and strength to tissues such as bone, tendon, skin and cartilage. Collagen constitutes one-third of the human proteome, providing mechanical stability, elasticity, and strength to organisms and is the prime construction material in biology. Collagen is also the dominating material in the extracellular matrix and its stiffness controls cell differentiation, growth, and pathology. However, the origin of the unique mechanical properties of collagenous tissues, and in particular its stiffness, extensibility, and nonlinear mechanical response at large deformation, remains unknown. By using X-ray diffraction data of a collagen fibril (Orgel, J. P. R. O. et al. Proc. Natl. Acad. Sci. 2006, 103, 9001) we can construct and simulate an experimentally validated model of the nanomechanics of a collagen microfibril that incorporates the full biochemical details of the amino acid sequence of constituting molecules and the nanoscale molecular arrangement. We found by direct mechanical testing that hydrated (wet) collagen microfibrils feature a Young's modulus of ≈300 MPa at small, and ≈1.2 GPa at larger deformation in excess of 10% strain, which is in excellent agreement with experimental data. We found that dehydrated (dry) collagen microfibrils show a significantly increased Young's modulus of ≈1.8-2.25 GPa, which is in agreement with experimental measurements and owing to tighter molecular packing. Here we show a simulated 10 ns time lapse of the collagen fibril atomistic model during equilibration. It shows the typical periodic banding (called "D-banding") which arise due to the staggering of molecules within the fibril. The close-up shows the fine atomistic details in the "overlap" region (the denser area) and then move to the "gap" region (the less dense area). The atomistic model of collagen fibril mechanics now enables the bottom-up elucidation of structure-property relationships in collagen materials (e.g., tendon, bone), including studies of genetic disease where the incorporation of biochemical details is essential. For more information, see: A. Gautieri, S. Vesentini , A. Redaelli, M.J. Buehler , "Hierarchical structure and nanomechanics of collagen microfibrils from the atomistic scale up," Nano Letters, Vol. 11(2), pp. 757-766, 2011 http://pubs.acs.org/doi/abs/10.1021/nl103943u