Crystal structure of the collagen triple helix model [(Pro‐Pro‐Gly)₁₀]₃

Abstract

The first report of the full-length structure of the collagen-like polypeptide [(Pro-Pro-Gly) 10 ] 3 is given. This structure was obtained from crystals grown in a microgravity environment, which diffracted up to 1.3 Å, using synchrotron radiation. The final model, which was refined to an R factor of 0.18, is the highestresolution description of a collagen triple helix reported to date. This structure provides clues regarding a series of aspects related to collagen triple helix structure and assembly. The strict dependence of proline puckering on the position inside the Pro-Pro-Gly triplets and the correlation between backbone and side chain dihedral angles support the propensity-based mechanism of triple helix stabilization/destabilization induced by hydroxyproline. Furthermore, the analysis of [(Pro-Pro-Gly) 10 ] 3 packing, which is governed by electrostatic interactions, suggests that charges may act as locking features in the axial organization of triple helices in the collagen fibrils.

Correlation between Raman and X-ray crystallography data of (Pro-Pro-Gly)10

“…Therefore, these bands reveal secondary structure features and hydration level. The peculiar absence of intra/inter chain H-bond in the (PPG) 10 structure implies a relevant effect of the hydration patter to define the super-assembly [1,6]. The position of three amide I bands in (PPG) 10 crystals (1629, 1645 and 1669 cm -1 ) is in good agreement with previous FT-IR absorption spectra of (PPG) 10 solution [29].…”

“…Here, up and down puckerings correspond to the negative and positive values of χ 1 dihedral angles, respectively. This strict dependence of proline puckering on its position in the triplet was first observed at 100 K inside the (PPG) 10 crystals for the inner proline residues [1], though the equivalent structure for (PPG) 9 revealed that five proline residues at the Y position are in a down puckering conformation [4].…”

“…Since crystals are isomorphous to those used for structural determination [1], the Raman crystallography study of (PPG) 10 provides the opportunity to define a relationship between vibrational properties and high-resolution structural details regarding both the φ and ψ torsional angles and the proline puckering.…”

“…(PPG) 10 is well characterized both from a structural [1] and a thermodynamic [2] point of view. Particularly, the melting temperature associated to the trimer disassembly is around 40 °C [2].…”

“…The low-resolution picture of (PPG) 10 shows a cylinder with length and diameter of 8.6 and 1.5 nm, respectively. The high resolution (1.3 Å) crystallographic structure of (PPG) 10 (Protein Data Bank code 1K6F) revealed accurate φ and ψ angles, and an alignment between chains driven by the charged extremity (N and C terminals) [1]. Based on high resolution structural information of (PPG) 10 [1], generalized as (X-Y-G) 10 , a new hypothesis was proposed for the extra stabilization induced by Hyp in Y [3].…”