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Abstract:
The molecular structure of collagen type 1 can be understood as the
result of evolutionary selection in the process of formation of calcium
phosphate based biocomposites acting as load bearing components in
living organisms. The evolutionary selection fulfills the principle of
'survival of the fittest' in a particular biological environment.
Disk-like post-nucleation complexes of Ca-2(HPO4)(3)(2-) organized in
ribbon-like assemblies in the metastable octacalcium phosphate (OCP)
phase, and Ca-3 triangles in the stable HAP phase had formed the
crystallographic motifs in this selection process. The rotational as
well as the translational symmetry of the major tropocollagen (TC) helix
agree nearly perfectly with the corresponding symmetries of the OCP
structure. The sequence of (Gly-X-Y) motifs of the three a chains
constituting the TC molecule enables an optimized structural fit for the
nucleation of Ca-3 triangles, the directed growth of nanostructured OCP,
and the subsequent formation of hydroxyapatite (HAP) in collagen
macrofibrils by a topotaxial transition. The known connection between
genetic defects of collagen type 1 and Osteogenesis imperfecta should
motivate the search for similar dependences of other bone diseases on a
disturbed molecular structure of collagen on the genetic scale.
