BiP maintains the permeability barrier of the ER membrane by sealing the lumenal end of the translocon pore before and early in translocation

Article Abstract:

Research was conducted to study the dynamics and structure of the translocon and the mechanism by which cotranslational protein translocation happens in mammalian endoplasmic reticulum membranes. Proteins bounded to ConA-Sepharose were pooled with those in the ATP-agarose flow-through fraction while soluble lumenal proteins were determined and purified in bulk. Results indicated that translocon pores existed in the absence of ribosomes in a different structure.

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Both lumenal and cytostolic gating of the aqueous ER transcolon pore are regulated from inside the ribosome during membrane protein integration

Article Abstract:

A series of fully assembled integration intermediates were prepared by in vitro translation in the presence of endoplasmic reticulum (ER) microsomes and signal recognition particles (SRPs). Analysis of the exposure of the nascent membrane to the cytosol and the ER lumen indicated the presence of an ordered and highly precise sequence that maintained the permeability barrier. Furthermore, structural changes on both sides of the ER maintained membrane integrity.

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Nascent membrane and secretory proteins differ in FRET-detected folding far inside the ribosome and in their exposure to ribosomal proteins

Article Abstract:

A transmembrane sequence within a nascent membrane protein folds into a compact confirmation near the peptidyltransferase is revealed by fluorescence resonance energy transfer (FRET) measurements. It remains folded as the sequence moves through a membrane bound ribosome into the translocor.

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