Crystal structure of the collagen model peptide (Pro-Pro-Gly)4-Hyp-Asp-Gly-(Pro-Pro-Gly)4 at 1.0 Å resolution

The single-crystal structure of the collagen-like peptide (Pro-Pro-Gly)4-Hyp-Asp-Gly-(Pro-Pro-Gly)4, was analyzed at 1.02 angstrom resolution. The overall average helical twist ( = 49.6 degrees) suggests that this peptide adopts a 7/2 triple-helical structure and that its conformation is very similar to that of (Gly-Pro-Hyp)9, which has the typical repeating sequence in collagen. High-resolution studies on other collagen-like peptides have shown that imino acid-rich sequences preferentially adopt a 7/2 triple-helical structure ( = 51.4 degrees), whereas imino acid-lean sequences adopt relaxed conformations ( < 51.4 degrees). The guest Gly-Hyp-Asp sequence in the present peptide, however, has a large helical twist ( = 61.1 degrees), whereas that of the host Pro-Pro-Gly sequence is small ( = 46.7 degrees), indicating that the relationship between the helical conformation and the amino acid sequence of such peptides is complex. In the present structure, a strong intermolecular hydrogen bond between two Asp residues on the A and B strands might induce the large helical twist of the guest sequence; this is compensated by a reduced helical twist in the host, so that an overall 7/2-helical symmetry is maintained. The Asp residue in the C strand might interact electrostatically with the N-terminus of an adjacent molecule, causing axial displacement, reminiscent of the D-staggered structure in fibrous collagens. (c) 2013 Wiley Periodicals, Inc. Biopolymers 99: 436447, 2013.