Summary
Highlights
Pre-procollagen, also known as collagen Alpha chains, is translated in the cytoplasm. The most crucial residue is glycine, often found in a glycine-X-Y pattern where X and Y are typically proline or lysine. Glycine is vital for the structural integrity of collagen.
This step occurs in the endoplasmic reticulum where proline and lysine residues are hydroxylated by the enzyme hydroxylase. This process absolutely requires vitamin C. A deficiency in vitamin C at this stage leads to scurvy. A mnemonic for this step is 'Hydroxyl-Lysine-C'.
Lysine hydroxyl groups get glycosylated, meaning sugars like galactose and glucose are added. Inadequate glycosylation of lysine hydroxyl groups can lead to osteogenesis imperfecta.
Three left-handed helices twist into a right-handed coil, forming procollagen. So far, the most important points for exams are glycine in step 1 and the vitamin C-dependent hydroxylation of proline and lysine in step 2.
Procollagen undergoes exocytosis, moving from inside the cell to the extracellular space. This step is a simple transport mechanism.
Disulfide-rich terminals on both sides of the three helices are cleaved by collagen peptidases, resulting in the formation of tropocollagen. A mnemonic for this is 'Cleave-S-S' (sevage with two S's), indicating disulfide cleavage. Problems in this step can lead to Ehlers-Danlos syndrome.
The enzyme lysyl oxidase, which is copper-dependent, covalently crosslinks the tropocollagen molecules into collagen fibrils. This establishes strong covalent bonds. A mnemonic for this is 'Cross-Lysine-ing' to remember lysyl oxidase. Issues with crosslinking can also cause Ehlers-Danlos syndrome and Menkes disease.