Heat shock protein 47 is a member of the serpin superfamily of serine proteinase inhibitors. Its expression is induced by heat shock. The protein localizes to the endoplasmic reticulum lumen and binds collagen; thus it is thought to be a molecular chaperone involved in the maturation of collagen molecules. Autoantibodies to this protein have been found in patients with rheumatoid arthritis. Colligins are characterized by an amino acid structure that includes an N-terminal hydrophobic signal sequence and 2 putative N-linked oligosaccharide attachment sites (Clarke et al., 1991). Colligins also have a C-terminal RDEL sequence that acts as an endoplasmic reticulum (ER) retention sequence. Other features permit the colligin-binding protein of ER to be classified as a serpin (serine-arginine protease inhibitor).