Type IV collagen, molecular model. Collagen is a long structural protein, formed from amino acids that make up polypeptide strands that twist around each other. Collagen is the most abundant protein in the human body and has a tough fibrous tensile strength. It is found throughout the body's connective tissues (skin, cartilage, bone, ligaments and tendons) providing structural and metabolic support. This is the NC1 domain in type IV collagen. This type of collagen forms sheets such as the basal lamina. This collagen molecule is based on that found in the lens capsule of a cow.