Type I collagen is a member of group I collagen (fibrillar forming collagen). Trimers of one alpha 2(I) and two alpha 1(I) chains. The C-terminal propeptide, also known as COLFI domain, have crucial roles in tissue growth and repair by controlling both the intracellular assembly of procollagen molecules and the extracellular assembly of collagen fibrils. It binds a calcium ion which is essential for its function (By similarity). Contains mostly 4-hydroxyproline. Proline residues at the third position of the tripeptide repeating unit (G-X-Y) are hydroxylated in some or all of the chains. Contains 3-hydroxyproline at a few sites. This modification occurs on the first proline residue in the sequence motif Gly-Pro-Hyp, where Hyp is 4-hydroxyproline. Lysine residues at the third position of the tripeptide repeating unit (G-X-Y) are 5-hydroxylated in some or all of the chains. O-glycosylated on hydroxylated lysine residues. The O-linked glycan consists of a Glc-Gal disaccharide. Belongs to the fibrillar collagen family.