The binding protein (BiP) and the synthesis of secretory proteins : Targeting and glycosylation of plant secretory proteins

The binding protein (BiP), a member of the heat-shock 70 family of molecular chaperones and a major resident of the endoplasmic reticulum, is found associated to variable extents with the newly-synthesized forms of many secretory proteins. In vivo and in vitro studies have shown that the mechanism of action of BiP involves ATPase activity and recognition of structural motifs that probably are exposed on the surface of newly synthesized proteins only before folding and assembly are completed. These observations strongly suggest that BiP functions in avoiding disordered aggregation of polypeptides during folding and assembly in the endoplasmic reticulum. BiP has also been involved as a component of the quality control mechanism that avoids intracellular transport of not yet matured and defective secretory proteins. While mammalian and yeast BiP are products of single genes, in some plants BiP is encoded by a multigene family. Whether the individual members of the family play distinct functions remains to be established.