BIOC 212 Lecture Notes - Lecture 34: Hydroxyproline, Disaccharide, Microfibril
29 May 2018
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Cell Junctions & Cell Adhesion XIV
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Formation of Collagen Fibrils
• Made in the cell as all other secreted proteins
o Ribosome translates mRNA into protein
o Ribosome docks on ER (RER), and then protein secreted into ER through
special channel as translated into protein
• For collagen, modifications occur immediately
1. Hydroxylation of selected prolines & selected lysines right away
2. Glycosylation of hydroxy-lysines
o Glycosylation for collagen is different than for other glycoproteins
o Collagen has small sugar moieties (galactose or galactose-glucose)
o Primitive glycosylation pattern
• As alpha chain matures, has certain parts (green, propeptide) important for:
1. Finding right three alpha chain
• Recognition sequences in C-terminal propeptide
• Wind around each other to form triple helix (similar to DNA)
o Propetides stay present --> important since:
2. Propeptides prevent intracellular aggregation
• After ER & Golgi, move further into secretory vesicles and secreted as
collagen triple helix
• Want to prevent multimerization (formation of large fibers) through
propeptides in secretory pathway
• If collagen was to multimerize, cell will burst/swell & die
• Collagen then secreted as triple helix in deep folds in the PM where
o Collagen secreted into extracellular space
• Through enzymatic mechanisms, propeptides are cleaved off
o Molecule has self-assembly recognition sites
o Get certain type of aggregation
o Result is formation of large collagen fibers containing multiple triple helices
• 100s, 1000s
• Collagen fiber can be 10-100s of nm thick
o Collagen fibers can laterally align to form even larger fibers (i.e. tendon, skin,
blood vessels)
o Self-assembly does not require any other proteins or enzymes
• Only need molecules finding each other
Formation of Fibrillar Collagens
• Different families of proteolytic enzymes, that cleave the propeptide off the
polypeptide sequence (N or C terminus)
