Transfer of Secretory Proteins through the Membrane of the Endoplasmic Reticulum

Abstract

Publisher Summary Secretory proteins are synthesized on ribosomes located in the cytoplasm and are released from the cell as a fairly homogeneous, highly concentrated population of molecules. Secretory proteins can be localized in the lumen of the endoplasmic reticulum (ER) very early in their existence. Translocation of secretory proteins from the cytoplasmic to the luminal side of the rough ER membrane is an essential feature of the transport of these molecules. The information for the association of the mRNAs encoding secretory proteins to the membrane is contained within secretory protein mRNAs itself. mRNA encoding a secretory protein contains the signal for its ultimate association with the membrane. All secretory protein mRNAs encode a transient N-terminal peptide. This short amino acid sequence provides a signal, which results in the formation of membrane-bound polysomes and, ultimately, the translocation across the membrane. This chapter presents the results of studies, which deal with various individual aspects of protein translocation. It also describes signal sequences, signal recognition particle, docking protein, ribosome binding, signal peptidase, and the cotranslational covalent modifications, which are carried out in the rough ER.