Molecular mechanics of mineralized collagen fibrils in bone

Bone is a natural composite of collagen protein and the mineral hydroxyapatite. The structure of bone is known to be important to its load-bearing characteristics, but relatively little is known about this structure or the mechanism that govern deformation at the molecular scale. Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities. We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils. Our results suggest that the mineral crystals within this network bears up to four times the stress of the collagen fibrils, whereas the collagen is predominantly responsible for the material’s deformation response. These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents.United States. Office of Naval Research (N000141010562)United States. Army Research Office (W991NF-09-1-0541)United States. Army Research Office (W911NF-10-1-0127)National Science Foundation (U.S.) (CMMI-0642545

Impact of Reduced Lignin on Plant Fitness

Lignin content of crop plants has been reduced by traditional plant breeding, natural and induced mutations, and insertion of transgenes. The effects of these genes and associated lower lignin content have been examined in terms of agricultural fitness or with regard to economically harvestable yields of useful plant products, or, in the case of some perennial species, survivability over multiple years. In general, crop yields are depressed by significant reductions in lignin content. Other negative effects observed in plants with lowered lignin contents include lodging and reduction of long-term survival of some perennial species. However, the interactions of genes involved in lignin metabolism with genetic background and the environment in which the low- lignin crop is cultivated are substantial. Examples are provided that demonstrate that lignin can be reduced in specific lines or populations without damaging fitness. It is concluded that it will be essential to incorporate lignin reducing genes into numerous genetic backgrounds and combinations, and evaluate the resulting lines in diverse environments, to discover optimal combinations and to obtain a true measure of value and fitness in agricultural systems