Average crystal structure of (Pro-Pro-Gly)(9) at 1.0 angstrom resolution

The average crystal structure of a collagen-model peptide, (Pro-Pro-Gly)(9) has been determined at 1.0 Angstrom resolution. Crystals belong to an orth orhombic system (P2(1)2(1)2(1)) with cell parameters of a = 26.82(2), b = 2 6.33(2). and c = 20.25(2)Angstrom. The X-Ray oscillation photograph clearly showed satellite spots with an 80 Angstrom axial repeat on both sides of t he strong spots on the layer lines corresponding to c = 20 Angstrom. The ex istence of c = 80 Angstrom axial repeat suggests that the longer repeat alo ng the c-axis is the shortest integral multiply of the helical repeat (20 A ngstrom) enough to accommodate one (Pro-Pro-Gly)(9) molecule and an appropr iate gap between adjacent molecules. According to the reflection data with c = 20 Angstrom axial repeat, the overall peptide structure is very close t o the left-handed 7/2-helical model for collagen. Based on the difference F ourier map, 34 water molecules were added in the asymmetric unit of seven t riplets. Of which 14 water molecules make hydrogen bonds with peptide chain s and rest of them participate in hydrogen bonds only with other water mole cules.