The Aqueous Pore through the Translocon Has a Diameter of 40–60 Å during Cotranslational Protein Translocation at the ER Membrane
نویسندگان
چکیده
Eukaryotic secretory proteins are cotranslationally translocated through the endoplasmic reticulum (ER) membrane via aqueous pores that span the lipid bilayer. Fluorescent probes were incorporated into nascent secretory proteins using modified Lys-tRNAs, and the resulting nascent chains were sealed off from the cytosol in fully assembled translocation intermediates. Fluorescence quenching agents of different sizes were then introduced into the ER lumen in order to determine which were small enough to enter the pore and to quench the fluorescence of probes inside the ribosome and/or the pore. These accessibility studies showed that the aqueous pore in a functioning translocon is 40-60 A in diameter, making it the largest hole observed to date in a membrane that must maintain a permeability barrier.
منابع مشابه
Both Lumenal and Cytosolic Gating of the Aqueous ER Translocon Pore Are Regulated from Inside the Ribosome during Membrane Protein Integration
Portions of the nascent chain are exposed to the lumen, the cytosol, or neither at different stages during the cotranslational integration of a protein into the ER membrane, as shown by compartment-specific collisional quenching of fluorophores incorporated into the polypeptide. The opening or closing of each end of the aqueous translocon pore is tightly controlled and occurs in a sequence that...
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ورودعنوان ژورنال:
- Cell
دوره 89 شماره
صفحات -
تاریخ انتشار 1997