title: Three-dimensional architecture of collagen type VI in the human trabecular meshwork.
abstract: OBJECTIVE
  Type VI collagen is a primary component of the extracellular matrix of many connective tissues. It can form distinct aggregates depending on tissue structure, chemical environment, and physiology. In the current study we examine the ultrastructure and mode of aggregation of type VI collagen molecules in the human trabecular meshwork.
  
  
  METHODS
  Trabecular meshwork was dissected from donor human eyes, and three-dimensional transmission electron microscopy of type VI collagen aggregates was performed.
  
  
  RESULTS
  Electron-dense collagen structures were detected in the human trabecular meshwork and identified as collagen type VI assemblies based on the three-dimensional spatial arrangement of the type VI collagen molecules, the 105-nm axial periodicity of the assemblies themselves, and their characteristic double bands, which arose from the globular domains of the type VI collagen molecules. Sulfated proteoglycans were also seen to associate with the assemblies either with the globular domain or the inner rod-like segments of the tetramers.
  
  
  CONCLUSIONS
  No extended structural regularity in the organization of type VI collagen assemblies within the trabecular meshwork was evident, and the lateral separation of the tetramers forming the assemblies varied, as did the angle formed by the main axes of adjacent tetramers. This is potentially reflective of the specific nature of the trabecular meshwork environment, which facilitates aqueous outflow from the eye, and we speculate that extracellular matrix ions and proteins might prevent a more tight packing of type VI collagen tetramers that form the assemblies.
authors.affiliation: Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Wales, UK.
authors.forename: Elena
authors.initials: E
authors.lastname: Koudouna
authors.affiliation: Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Wales, UK.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Young
authors.affiliation: Department of Ophthalmology, Kyoto Prefectural University of Medicine, Hirokoji Kawaramachi, Kyoto, Japan.
authors.forename: Morio
authors.initials: M
authors.lastname: Ueno
authors.affiliation: Department of Ophthalmology, Kyoto Prefectural University of Medicine, Hirokoji Kawaramachi, Kyoto, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kinoshita
authors.affiliation: Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Wales, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Quantock
authors.affiliation: Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Wales, UK.
authors.forename: Carlo
authors.initials: C
authors.lastname: Knupp
mesh_terms: D000368:Aged; D024142:Collagen Type VI / Q000737:chemistry / Q000648:ultrastructure*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D014054:Tomography; D014129:Trabecular Meshwork / Q000648:ultrastructure*
chemical_list: D024142:Collagen Type VI