The in situ conformation and axial location of the intermolecular cross-linked non-helical telopeptides of type I collagen.
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 on to 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 alpha1 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.
Orgel
J P
JP
Department of Biological Science, University of Stirling, Stirling, FK9 4LA, UK.
Wess
T J
TJ
Miller
A
A
D001665:Binding Sites; D003094:Collagen / Q000737:chemistry* / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D014961:X-Ray Diffraction
D010446:Peptide Fragments; D003094:Collagen