Unique side-chain conformation encoding for chirality and azimuthal orientation in the molecular packing of skin collagen.

We used molecular mechanics to study the role of gly X-Y+ sequences, where X- was Asp or Glu and Y+ was Lys or Arg, in the molecular packing of type I collagen. In the minimal energy conformation of a triply stranded molecule having a coiled-coil configuration, the side-chains of these sequences segregated into two oppositely charged groupings of the forms X-Y+X- and Y+X-Y+. Groupings having the same net charge were clustered along two complementary azimuthal edges of the molecule. Intermolecular interactions, through these oppositely charged edges, align the molecules appropriately for the formation of the HHL crosslink of skin. This alignment also can account for the axial periodicity and chiral appearance of skin collagen fibrils.