Proline provides site-specific flexibility for in vivo collagen

Wing Ying Chow,David G Reid,Lucy J Colwell,Rakesh Rajan,David J Wales,Anna M Puszkarska,Melinda J Duer,David A Slatter,Chris J Forman,Richard W Farndale,Dominique Bihan

doi:10.1038/s41598-018-31937-x

Abstract

Fibrillar collagens have mechanical and biological roles, providing tissues with both tensile strength and cell binding sites which allow molecular interactions with cell-surface receptors such as integrins. A key question is: how do collagens allow tissue flexibility whilst maintaining well-defined ligand binding sites? Here we show that proline residues in collagen glycine-proline-hydroxyproline (Gly-Pro-Hyp) triplets provide local conformational flexibility, which in turn confers well-defined, low energy molecular compression-extension and bending, by employing two-dimensional 13C-13C correlation NMR spectroscopy on 13C-labelled intact ex vivo bone and in vitro osteoblast extracellular matrix. We also find that the positions of Gly-Pro-Hyp triplets are highly conserved between animal species, and are spatially clustered in the currently-accepted model of molecular ordering in collagen type I fibrils. We propose that the Gly-Pro-Hyp triplets in fibrillar collagens provide fibril “expansion joints” to maintain molecular ordering within the fibril, thereby preserving the structural integrity of ligand binding sites.

Highlights

The dominant protein components of the extracellular matrix are ordered fibrillar collagens
The hydroxylation of a Yaa position P, occurring immediately after synthesis of the collagen precursors, causes the resulting O ring to strongly favour the exo conformation, which in turn pre-organises the peptide chain structure at the O residues towards the polyproline II helix that is required in each strand of the collagen triple helix; GPO triplets in collagens are widely viewed as being essential for triple helix folding and stabilizing the triple helix structure[5,6]
Solid-state NMR spectroscopy provides an accurate method for assessing the distribution of collagen proline ring endo-exo conformations in intact tissues

Summary

Introduction

The dominant protein components of the extracellular matrix are ordered fibrillar collagens. The X-position P rings (PX) in GPO triplets of short model collagen peptides occupy metastable structures, and endo and exo ring conformations (Fig. 1) are almost favoured at biologically-relevant temperatures.

Results

Conclusion