Protein folding in the secretory pathway of animal cells

The exit of newly-synthesized proteins from the lumen of the endoplasmic reticulum (ER) is the rate-determining step in protein secretion. Only correctly-folded and fully-assembled proteins exit the ER and progress along the secretory pathway. Folding and assembly in the ER are mediated by a variety of factors including folding catalysts and molecular chaperones. The properties of these factors, and the nature of their interactions with folding substrates, are beginning to be clarified. Little work has been done to characterize these processes and these factors in cell lines employed for large-scale cell culture. Manipulation of these process may permit improvement in yield or productivity of recombinant proteins by cultured animal cells.