title: Structure of type I and type III heterotypic collagen fibrils: an X-ray diffraction study.
abstract: The molecular packing arrangement within collagen fibrils has a significant effect on the tensile properties of tissues. To date, most studies have focused on homotypic fibrils composed of type I collagen. This study investigates the packing of type I/III collagen molecules in heterotypic fibrils of colonic submucosa using a combination of X-ray diffraction data, molecular model building, and simulated X-ray diffraction fibre diagrams. A model comprising a 70-nm-diameter D- (approximately 65 nm) axial periodic structure containing type I and type III collagen chains was constructed from amino acid scattering factors organised in a liquid-like lateral packing arrangement simulated using a classical Lennard-Jones potential. The models that gave the most accurate correspondence with diffraction data revealed that the structure of the fibril involves liquid-like lateral packing combined with a constant helical inclination angle for molecules throughout the fibril. Combinations of type I:type III scattering factors in a ratio of 4:1 gave a reasonable correspondence with the meridional diffraction series. The attenuation of the meridional intensities may be explained by a blurring of the electron density profile of the D period caused by nonspecific or random interactions between collagen types I and III in the heterotypic fibril.
authors.affiliation: Centre for Extracellular Matrix Biology, Department of Biological Sciences, University of Stirling, Scotland, United Kingdom. g.j.cameron@stir.ac.uk
authors.forename: G J
authors.initials: GJ
authors.lastname: Cameron
authors.forename: I L
authors.initials: IL
authors.lastname: Alberts
authors.forename: J H
authors.initials: JH
authors.lastname: Laing
authors.forename: T J
authors.initials: TJ
authors.lastname: Wess
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D024042:Collagen Type I / Q000737:chemistry* / Q000648:ultrastructure; D024061:Collagen Type III / Q000737:chemistry* / Q000648:ultrastructure; D003106:Colon / Q000378:metabolism; D024022:Fibrillar Collagens / Q000737:chemistry* / Q000648:ultrastructure; D007413:Intestinal Mucosa / Q000378:metabolism; D008958:Models, Molecular; D051381:Rats; D012542:Scattering, Radiation; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D024042:Collagen Type I; D024061:Collagen Type III; D024022:Fibrillar Collagens