Type XXI Collagen

Type XXI collagen belongs to the fibril-associated collagens with interrupted triple helices (FACIT) family of collagen proteins. Type XXI collagen may copolymerize with fibrillar collagens via their C-terminal collagenous domains and mediate protein–protein interactions through their N-terminal noncollagenous domains, thereby serving as molecular bridges in the extracellular matrix. Type XXI collagen is expressed in heart, placenta, stomach, jejunum, skeletal muscle, kidney, lung, pancreas, and lymph node. Currently, there are no known mutations in humans and mice null mutation work has not been reported. The biological function of type XXI collagen remains to be revealed; however, data suggest that type XXI collagen may play a role in blood vessel assembly. Biomarkers need to be developed to determine the function and relevance under pathological conditions.