Interpretation of the small-angle X-ray diffraction of collagen in view of the primary structure of the alpha1 chain

The small-angle X-ray diffraction pattern of collagen has been calculated using the sequence of the alpha 1 chain and a Hodge-Petruska scheme for the packing of the collagen molecules. The molecular stagger giving the best fit of calculated-to observed structure factors has been found to be 236 or 237 amino acid residues for three tendon collagens. But this result depends on the appoximation that the molecular conformation is uniform throughout the molecule. A comparison of the observed and calculated electron density profiles in axial projection leads to a corrected model, in which the COOH-terminal telopeptide is contracted in a way suggesting a saddle-shaped electron density distribution near the collagenase site