The structure of elastoidin in relation to that of tendon collagen

Molecular tilting in dried elastoidin and its implications for the structures of other collagen fibrils

Wet elastoidin spicules (fish fin rays) yield low-angle meridional X-ray diffraction patterns which resemble those from tendons. However, when the spicule dries the meridian splits into the arms of a diagonal cross (sometimes only one arm appears). Of the possible explanations we reject shearing of the axial arrangement of molecules but confirm tilting. We suggest that, in three dimensions, the molecules are tilted at angles which vary from 0 degrees at the centre to some maximum value at the surface of the spicule, resembling torsion of the array of molecules. Molecular tilting probably occurs in other collagen fibrils.

Structure and packing of dry elastoidin: a collagen phase change

Wide angle X-ray patterns of wet shark fin elastoidin always show a very intense meridional streak arising from the small angle diffraction pattern. When the fin ray spicules (ceratotrichia) are permitted to air dry, the pattern departs from the meridian. Studies show that the dry spicules are, in fact, radially anisotropic. Diffraction patterns taken with the X-ray beam perpendicular to the edge of the ribbon-shaped spicules have two distinct arms (with an interarm angle of as much as 70 degrees), while the small angle streak taken with the beam perpendicular to the ribbon face is generally either on the meridian, or is so weak that it cannot be resolved from the background. An analysis of the intensities of the small angle diffraction pattern of the dry form indicate that it has essentially a normal dry collagen structure. Addition of methanol serves only to expand the dry structure, without reversal of the phase transition. These data can be interpreted by postulating that as the wet structure collapses during drying, the collagen molecules tilt in a direct perpendicular to the face of the ribbon, forming domains of molecules with similar axial orientation. The implication is that the original interactions are lost, and the new structure is formed by overlaps between formerly non-interacting molecules.

X-ray diffraction effects related to superstructure in rat tail tendon collagen

A number of unusual X-ray diffraction effects concerning the meridional low angle reflections of collagen are presented which are due to structural inhomogeneities in the 100 micron range within the tendon such as are expected to be associated with the planar crimp structure of tendon units. These newly observed effects provide diffraction confirmation for such a crimped morphology. The effects consist of splitting of the reflections both azimuthally and radially. Azimuthal split varied with rotation of the tendon unit around its own axis and is directly related to the existence of the crimp, its angle and planarity. Radial splitting is a consequence of the limited sampling of the micro-structure by the collimator, which provides further support for the crimp morphology and conveys added information about the crimp form. It is shown that this limited sampling can provide a kind of "micro-X-ray topography" technique for the study of micro-textures on the appropriate dimensional level, while ti could be the source of misrepresentation if its origin remains unrecognized. The effect of stretching is examined and interpreted in terms of crimp straightening. Simultaneous examination of medium angle equatorial reflections, when combined with some electron micrographs point to further issues concerning the relation between the large scale and fibril substructure. It is believed that the present findings have general implications for structure research on collagen.