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The in situ conformation and axial location of the intermolecular cross- linked non-helical telopeptides of type I collagen
Journal article   Peer reviewed

The in situ conformation and axial location of the intermolecular cross- linked non-helical telopeptides of type I collagen

J P R O Orgel, Tim J Wess and Andrew Miller
Structure, Vol.8(2), pp.137-142
2000
DOI: https://doi.org/10.1016/S0969-2126(00)00089-7
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https://doi.org/10.1016/S0969-2126(00)00089-7View
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Abstract

collagen fibril molecular packing structure telopeptide X-ray diffraction
Background: Type I collagen contains specific lysine and hydroxylysine residues that are critical in the formation of intermolecular cross-links crucial for the normal configuration and stability of the 67 nm axial repeat of collagen fibrils in the extracellular matrix. The major cross-linkage sites are believed to occur between the non-helical terminal regions (telopeptides) and helical segments of adjacent collagen molecules. In this X-ray fibre diffraction study the tissue has been maintained in the hydrated fibrillar state, whilst detailed structural information was obtained using highly collimated synchrotron radiation. Results: The axial component of the X-ray diffraction patterns extends more than twice as far in reciprocal space than that of any already published. The structure-factor phases were calculated using the multiple isomorphous addition method, avoiding model- based approaches, and produced an electron-density profile of the molecular arrangement projected onto the fibre axis to 0.54 nm resolution. This corresponds to the phasing of 124 orders of the meridional diffraction pattern. Conclusions: The axially projected electron-density profile and the electron-density difference maps showed that both the N- and C-terminal telopeptides are contracted structures. This profile puts narrow constraints on the possible conformations of the C-terminal telopeptide; the best fit to the electron-density profile is when the α1 chains adopt a folded conformation with a sharp hairpin turn around residues 13 and 14 of the 25- residue telopeptide. Our results reveal for the first time the location, parallel to the fibril axis, of the intermolecular cross-links in normal hydrated tissue. These cross-links are essential for the biological function of the tissue.

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