Article Figures & Tables
Figures
- Table 1.
The collagen family of proteins
Collagen type Genes Supramolecular organization in tissues (where known) References I COL1A1 Fibrils in tendon, bone, skin, cornea and blood vessel walls Chu et al., 1982 COL1A2 Myers et al., 1981 II COL2A1 Fibrils in cartilage Miller and Matukas, 1969 III COL3A1 Forms heterotypic fibrils with type I collagen Cameron et al., 2002 IV COL4A1 Network in basement membrane Timpl and Brown, 1996; Timpl et al., 1981 COL4A2 COL4A3 COL4A4 COL4A5 COL4A6 V COL5A1 Forms heterotypic fibrils with type I Birk, 2001 COL5A2 COL5A3 VI COL6A1 Fine microfibrils with ubiquitous distribution (distinct from fibrillin-containing microfibrils Kielty et al., 1992 COL6A2 COL6A3 VII COL7A1 Forms anchoring fibrils in skin at the dermal/epidermal junction (basement membrane) Keene et al., 1987 VIII COL8A1 3D hexagonal lattice in Descemet's membrane in the eye Kapoor et al., 1986; Kapoor et al., 1988; Stephan et al., 2004 COL8A2 IX COL9A1 Associated with type II collagen fibrils Olsen, 1997; Shimokomaki et al., 1990 COL9A2 X COL10A1 Mat-like structure/hexagonal lattice in the hypertrophic zone of the growth plate Kwan et al., 1991 XI COL11A1 Forms heterotypic fibrils with type II Mendler et al., 1989 COL11A2 COL2A1 XII COL12A1 Associated with type I fibrils Keene et al., 1991; Nishiyama et al., 1994; Zhang et al., 2003 XIII COL13A1 Transmembrane and possibly involved in cell adhesion Latvanlehto et al., 2003 XIV COL14A1 Associated with type I fibrils Young et al., 2000b; Young et al., 2002 XV COL15A1 Specialized basement membranes, cleaved to produce antiangiogenic fragment (restin) Myers et al., 1996; Ramchandran et al., 1999 XVI COL16A1 Component of specialized fibrillin-rich microfibrils in skin and type II collagen fibrils in cartilage Kassner et al., 2003 XVII COL17A1 Transmembrane component of hemidesmosomes (cell-cell junctions), which attach epidermis to basement membrane in skin Hopkinson et al., 1998 XVIII COL18A1 Cleaved to produce antiangiogenic fragment (endostatin) Sasaki et al., 1998 XIX COL19A1 Radially distributed aggregates formed by association at one end in vitro Myers et al., 2003 XX COL20A1 May be associated with type I collagen fibrils Koch et al., 2001 XXI COL21A1 May be fibril associated, widespread expression pattern Fitzgerald and Bateman, 2001 XXII COL22A1 Located in specific tissue junctions and may be associated with microfibrils Koch et al., 2004 XXIII COL23A1 Transmembrane collagen identified in cell culture Banyard et al., 2003 XXIV COL24A1 Expressed in tissues containing type I collagen Koch et al., 2003 XXV COL25A1 Transmembrane collagen, cleaved form present in Alzheimer's amyloid plaques in neurons Hashimoto et al., 2002 XXVI COL26A1 Expressed in testis and ovary of adult tissues Sato et al., 2002 XXVII COL27A1 Widespread expression particularly in cartilage Boot-Handford et al., 2003; Pace et al., 2003 - Fig. 1.
Transmission electron microscopy of cultured embryonic tendon fibroblasts shows randomly orientated extracellular collagen fibrils. A: bar, 2 μm; B: bar, 1 μm.
- Fig. 2.
Overview of the steps involved in the production of collagen fibrils by fibroblasts. Procollagen chains are synthesized in the endoplasmic reticulum (ER), are brought together by interactions between the C-propeptides and fold to form a rod-like triple-helical domain flanked by globular N- and C-propeptides. The large number of post-translational modifications that occur in the ER are not depicted. Removal of the N- and C-propeptides from fully folded procollagen only occurs after transport of procollagen across the Golgi stacks and results in collagen molecules that are then able to assemble into fibrils. Covalent crosslinks occur within and between triple-helical collagen molecules in fibrils.
- Table 2.
Location of enzymes involved in the modification of N-linked oligosaccharides within the Golgi stacks *
Cisternal location Enzyme Cis α mannosidase I Medial N-acetylglucosaminyl transferase I Medial α mannosidase II Medial N-acetylglucosaminyl transferase II Medial Fucosyltransferase Trans Galactosyltransferase Trans Sialytransferase -
↵* The number of cisternae in the Golgi stacks is variable and each cisternal location might comprise 2-3 individual cisternae.
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- Fig. 3.
The fibripositor secretory pathway. (A) Transmission electron microscopy of transverse sections through embryonic mouse tail tendon shows bundles of extracellular collagen fibrils between adjacent cells. One (a), two (b), three (c) or more (not shown) membrane-bounded collagen fibrils are also frequently observed within the cytoplasm. Membrane-bounded collagen fibrils are also observed in plasma membrane (PM) extensions called fibripositors (d). Bar, 500 nm. (B-D) Schematics showing longitudinal representations of collagen fibrils in (B) a Golgi-to-PM transport compartment (GPC+cf) and within both (C) closed and (D) open fibripositors. The topology of membrane-bounded collagen fibrils observed in cross-section and the PM was determined by serial-section 3D reconstruction. Selected potential planes of section are represented by dotted lines. (a-c) Cross-section through one (a), two (b) and three (c) fibrils located within the cytoplasm; (d) cross-section through a single fibril located within a fibripositor.
- Fig. 4.
Schematic of the activation pathway for the procollagen N- and C-proteinases. This enzyme cascade is initiated by autocatalytic activation of furin or furin-like proprotein convertases in the trans-Golgi network and is responsible for the processing of procollagen to collagen by ADAMTS (N-proteinase) and tolloid (C-proteinase) family enzymes. Amino acid sequences cleaved by furin are shown between the pro- and catalytic domains of the enzymes. The signal sequence for secretory targeting is represented as a black rectangle. Abbreviations: ADAMTS, a disintegrin and metalloproteinase with thrombospondin motifs; BMP-1, bone morphogenetic protein 1; CUB domains, so-called owing to their occurrence in complement components, a sea urchin protein and BMP-1; EGF, epidermal growth factor; mTLD, mammalian tolloid; P-domain, region required for processing activity; Pro, prodomain, removal of which is required for enzyme activation; TLL-1, tolloid like 1; TSP, thrombospondin.
Article navigation
- Top
- Article
- Summary
- Introduction
- Collagen is an abundant component of the ECM
- Collagen biosynthesis
- Collagen trafficking
- Extrusion of collagen fibrils
- Procollagen processing
- The role of cell-surface proteins in collagen fibrillogenesis
- Extracellular collagen fibril growth
- Trafficking and assembly of fibril-associated molecules
- Conclusions and future goals
- Acknowledgements
- References
- Figures & tables
- Info & metrics
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