Collagen alpha-2(XI) chain is a protein that in humans is encoded by the COL11A2 gene. The COL11A2 gene produces one component of this type of collagen, called the pro-alpha2(XI) chain. Type XI collagen adds structure and strength to the tissues that support the body's muscles, joints, organs and skin (the connective tissue). Type XI collagen is normally found in cartilage as well as the fluid that fills the eyeball, the inner ear, and the center portion of the discs between the vertebrae in the spine (nucleus pulposus). Type XI collagen also helps maintain the spacing and diameter of type II collagen fibrils. Type II collagen is an important component of the eye and mature cartilage tissue. The size and arrangement of type II collagen fibrils is essential for the normal structure of these