Glycosylation of hydroxylysyl residues

Occur in part in globular conformation and in short triplehelical structure 

The 4-hydroxylation of at least 100 prolyl residues per proa chain  

The formation of interchain disulfide linkages in the C-terminal propeptide. The latter cannot be formed until translation is nearly finished. The rate of disulfide bond and triple-helix formation varies greatly from one cell type to another—only minutes in tendon cells that synthesize type I collagen but an hour in cells that synthesize basement membrane collagen. These differences in synthesis time may account for the variations in hydroxylation and glycosylation. Thus, the extent of posttranslational modifications depends not only on levels of enzyme and cofactors but also on the time available. 

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