Biology: Collagen and Fibronectin Synthesis

Collagen Synthesis

• 28 types of collagen have been identified in vertebrates
• Collagen molecules form a triple-stranded helix, which can assemble into supramolecular complexes like fibrils and networks
• Fibrous collagens form the backbone of collagen fibril bundles in interstitial tissue stroma
• Network collagens are incorporated into the basal membrane (BM)

Post-Translational Modifications in Collagen Synthesis

• Synthesis of collagen type I involves enzymatic post-translational modifications
• Modifications include hydroxylation of proline and lysine residues, glycosylation of lysine, and cleavage of N- and C-terminal propeptides

Collagen Fibril Formation

• Collagen fibrils are strengthened by covalent crosslinking between lysine residues of constituent collagen molecules by lysyl oxidases (LOX)

Fibronectin Synthesis and Assembly

• Fibronectin (FN) is secreted as a dimer joined by two C-terminal disulfide bonds
• FN has binding sites for other FN dimers, collagen, heparin, and cell-surface integrin receptors
• Cell-surface binding of soluble FN dimer is essential for its assembly into longer fibrils
• Cell contraction through the actomyosin cytoskeleton and integrin clustering promotes FN–fibril assembly