May play an important role in fibrillogenesis by controlling lateral growth of collagen II fibrils. Trimers composed of three different chains: alpha 1(XI), alpha 2(XI), and alpha 3(XI). Alpha 3(XI) is a post-translational modification of alpha 1(II). Alpha 1(V) can also be found instead of alpha 3(XI)=1(II). Additional isoforms seem to exist. There is alternative usage of exon IIA or exon IIB. Transcripts containing exon IIA or IIB are present in cartilage, but exon IIB is preferentially utilized in transcripts from tendon. Cartilage, placenta and some tumor or virally transformed cell lines. Isoforms using exon IIA or IIB are found in the cartilage while isoforms using only exon IIB are found in the tendon. 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). Prolines at the third position of the tripeptide repeating unit (G-X-Y) are hydroxylated in some or all of the chains. N-glycosylated. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease may be caused by variants affecting the gene represented in this entry. Belongs to the fibrillar collagen family.