Crystal and Molecular Structure of a Collagen-Like Peptide at 1.9 Å Resolution

Abstract

The structure of a protein triple helix has been determined at 1.9 angstrom resolution by x-ray crystallographic studies of a collagen-like peptide containing a single substitution of the consensus sequence. This peptide adopts a triple-helical structure that confirms the basic features determined from fiber diffraction studies on collagen: supercoiling of polyproline II helices and interchain hydrogen bonding that follows the model II of Rich and Crick. In addition, the structure provides new information concerning the nature of this protein fold. Each triple helix is surrounded by a cylinder of hydration, with an extensive hydrogen bonding network between water molecules and peptide acceptor groups. Hydroxyproline residues have a critical role in this water network. The interaxial spacing of triple helices in the crystal is similar to that in collagen fibrils, and the water networks linking adjacent triple helices in the crystal structure are likely to be present in connective tissues. The breaking of the repeating (X-Y-Gly)n pattern by a Gly-->Ala substitution results in a subtle alteration of the conformation, with a local untwisting of the triple helix. At the substitution site, direct interchain hydrogen bonds are replaced with interstitial water bridges between the peptide groups. Similar conformational changes may occur in Gly-->X mutated collagens responsible for the diseases osteogenesis imperfecta, chondrodysplasias, and Ehlers-Danlos syndrome IV.

Triple‐helical peptides: An approach to collagen conformation, stability, and self‐association

“…21,22 These hydrogen bonded networks often adopt pentagonal arrangements of water and are anchored to the peptide chain through backbone carbonyls and hydroxyl groups of Hyp ( Figure 1a). The observation of Hyp involvement in a hydrogen-bonded water network is consistent with that proposed by Ramachandran's group on the basis of modeling and Privalov on the basis of calorimetry studies on collagens.…”

“…In many of the crystal structures, triple-helical peptides show quasi-hexagonal packing and intermolecular distances similar to that of collagen molecules in fibrils. 21,26 Water-mediated interactions and Hyp-Hyp intermolecular hydrogen bonding are involved in the lateral packing of peptides. Such triple-helix to triple-helix interactions are consistent with the conclusions of the Leikin laboratory, based on X-ray diffraction of tendon under different osmotic pressures, that hydration provides a major force for collagen fibrillogenesis.…”

“…45 The crystal structure of a (Pro-Hyp-Gly) 10 peptide containing one Gly to Ala replacement shows a loss of direct hydrogen bonds at the Ala site, a local untwisting of the helix, and a loss of register between the two triple-helical ends. 21 OI collagens with a Gly missense mutation have a delay in folding 46 and model peptides indicated that such a Gly replacement will arrest C-to N-terminal triple-helix folding unless there is a strong renucleation site downstream of the mutation. 47 It is interesting to note that Gly replacement mutations in nonfibrillar collagens also lead to pathological conditions even though a perfect (Gly-X-Y) n repeating pattern is not found in their natural triple-helix.…”

Folding defects in fibrillar collagens

“…Substitutions for glycine residues alter the triple helical structure (Bella et al 1994;Baum & Brodsky 1999;Klein & Huang 1999) and produce delay in triple-helix formation. The helix appears to propagate normally from the region of nucleation at the carboxy-terminal end to the domain of the mutation, where it either ceases or slows at 37 8C (Raghunath et al 1994).…”

Collagen pretzels revealed by electron microscopy

“…X-ray fibre diffraction studies in the 1950s and recent X-ray crystallography of collagen-like peptides have provided information about the collagen triple helix at atomic resolution (for reviews, see [1,2]). However, most collagens function as part of supramolecular assemblies, which are refractory to study by conventional high-resolution techniques.…”