MOLECULAR PACKING OF TYPE-I COLLAGEN IN TENDON

X-ray diffraction of rat tail tendon shows that type I collagen fibril s contain regions of three-dimensional crystalline arrays; where molec ular packing is speculated to be by a staggered sheet or microfibril a rrangement. The X-ray diffraction pattern also contains a significant amount of diffuse scatter indicative of static and thermal disorder in fibrils. Removal of the diffuse scatter from the equatorial region of X-ray diffraction patterns obtained using synchrotron radiation allow ed the Bragg intensities to be viewed on a flat background. Indexing o f Bragg peak intensity on the 10, -10, 0-1, 01, -11 and 1-1 row-lines of the triclinic unit cell have been used here to test possible sheet and microfibril packing arrangements. The relative translation of mole cular segments in the gap and overlap regions as well as the telopepti de orientation have been investigated. A global search through combina tions of molecular packing and molecular translation revealed that the sheet-type conformations cannot account for the observed low-angle of f-meridional Bragg peak intensity distribution. A superior fit is obta ined with D-staggered left-handed microfibril structures. The orientat ion of the telopeptides may indicate that there are interconnections b etween microfibrils that may explain the difficulty in isolating indiv idual microfibrillar structures. (C) 1998 Academic Press Limited.