Type XII collagen interacts with type I collagen-containing fibrils, the COL1 domain could be associated with the surface of the fibrils, and the COL2 and NC3 domains may be localized in the perifibrillar matrix. Trimer of identical chains each containing 190 kDa of non-triple-helical sequences. Additional isoforms seem to exist. The triple-helical tail is stabilized by disulfide bonds at each end. Hydroxylation on proline residues within the sequence motif, GXPG, is most likely to be 4-hydroxy as this fits the requirement for 4-hydroxylation in vertebrates. O-glycosylated; glycosaminoglycan of chondroitin-sulfate type. Belongs to the fibril-associated collagens with interrupted helices (FACIT) family.