COL9A1, which is short for Collagen alpha-1(IX) chain, is a 921 aa. protein. It is a secreted protein, and exists in extracellular space and extracellular matrix. This protein is a heterotrimer of an alpha 1(IX), an alpha 2(IX) and an alpha 3(IX) chain.Each subunit is composed of three triple-helical domains interspersed with non-collagenous domains. The globular domain at the N-terminus of type IX collagen molecules represents the NC4 domain which may participate in electrostatic interactions with polyanionic glycosaminoglycans in cartilage. It ia a structural component of hyaline cartilage and vitreous of the eye.