The NC4 domain of the cartilage-specific collagen IX inhibits complement directly due to attenuation of membrane attack formation and indirectly through binding and enhancing activity of complement inhibitors C4B-binding protein and factor H.
Collagen IX containing the N-terminal non-collagenous domain 4 (NC4) domain is unique to cartilage and a member of the family of fibril-associated collagens with both collagenous and non-collagenous domains. Collagen IX is located at the surface of fibrils formed by collagen II and a minor proportion of collagen XI, playing roles in tissue stability and integrity. The NC4 domain projects out from
