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). Isoforms lack exons 6, 7 or 8 or a combination of these exons. Experimental confirmation may be lacking for some isoforms. 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. A disulfide-bonded peptide called proline/arginine-rich protein or PARP is released from the N-terminus during extracellular processing and is subsequently retained in the cartilage matrix from which it can be isolated in significant amounts. 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 is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the fibrillar collagen family. Gene page