Molecular Structure of Type II Collagen

Abstract

The naturally crystalline arrangement of collagen molecules within the fibrils of some tissues, allows the use of fiber diffraction methods for structural characterization. This method has the potential to give structural information about collagen type II with minimum interference from sample preparation and may give the opportunity to produce relatively detailed three-dimensional visualization of the fibrils sub-structure. Towards this end, experiments with Multiple Isomorphous Replacement (MIR) were carried out to so that a one-dimensional electron density map of native collagen structure may be determined. Several experiments were performed at the BioCAT facility at Argonne National Laboratory with variations of: sample holder designs, sample preparation procedures, heavy atoms for MIR, temperatures and setups for small and medium angle diffraction. Some more optimum combinations of these produced data of resolution 15 A or better in the axial direction. Using these data, a subsequent study that also made use of AFM and TEM techniques, revealed that the parameters of collagen type II fibrils from lamprey notochord are very similar if not the same as collagen type II fibrils in mammalian tissues: 30 nm in diameter, axial periodicity of 67 nm, amino acid charge distribution is the same. Analysis of the X-ray diffraction derived one dimensional electron density map showed that the telopeptides, which are crucial for fibrillogenesis and organization of collagen type II tissues, have a very specific folded conformation, reminiscent of that seen in the C-telopeptide of type I collagen. The folded telopeptide conformations provide a clear picture of the intermolecular crosslink locations within the contributing collagen monomers within the 67 nm D-period. This type of structural information is essential for understanding the mechanisms of tissue development and disease pathologies.