Polypeptide translocation across the endoplasmic reticulum membrane

• Published in: The Journal of biological chemistry Vol. 267; no. 20; pp. 13791 - 13794
• Main Authors: SANDERS, S. L, SCHEKMAN, R
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 15-07-1992
• Subjects: Animals; Biological and medical sciences; Cell physiology; endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Fundamental and applied biological sciences. Psychology; Membrane and intracellular transports; Membrane Proteins - metabolism; membranes; Models, Biological; Molecular and cellular biology; Peptides - metabolism; polypeptides; Proteins - metabolism; Receptors, Cell Surface - metabolism; Receptors, Cytoplasmic and Nuclear; reviews; translocation; Proteins; Polypeptide; Secretion; Reaction mechanism; Review; Endoplasmic reticulum; Membrane translocation; Carrier protein
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)49634-8

Many polypeptides have been postulated to play direct roles in secretory protein translocation based on genetic criteria,
cross-linking, and antibody inhibition. Much of the excitement in the next few years will come from the resolution of current
controversies. What is the nature of the ribosome receptor, and is it essential for translocation? Is BiP required for translocation
in mammalian cells? Are all of the polypeptides of signal peptidase and oligosaccharyltransferase required for catalytic function,
or do some of them mediate steps of protein translocation? One of the best ways to resolve these problems will be to determine
the importance of each in reconstituted translocation reactions by fractionation or immunodepletion, or by analysis in a purified
reaction. Another approach is to identify homologues of these molecules in S. cerevisiae and to assess their importance in
in vivo translocation. Several mechanistic questions remain to be addressed as well. Does the protein translocation apparatus
consist of protein, or lipid, or both? How are integral membrane proteins inserted? How is the translocon gated to admit only
unfolded or partially folded secretory polypeptides and to exclude cytoplasmic molecules? The answers to these questions will
illuminate a basic enigma in cell biology that has remained unanswered for many years.