Two stress proteins of the endoplasmic reticulum bind denatured collagen

A differentiation-related gelatin-binding 46 kilodalton (kDa) glycoprotein in myoblasts (GP46, colligin) shares several properties with the 78-kDa glucose-regulated protein (GRP78), including location in the endoplasmic reticulum and related C-terminal sequences. These similarities extend to stress inducibility, since we find that GP46 is a heat-shock protein; its synthesis is elevated at 42 degrees C, resulting in a two- to three-fold increase in protein level. Further, GRP78 is a gelatin-binding protein; together with GP46 it is retained on gelatin-Sepharose beads. GRP78 and GP46 do not interact; each protein can be individually eluted, GP46 at low pH and GRP78 by ATP. These results suggest that the proteins have distinct roles in the synthesis of collagen and point to a simple method for purification.