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

Cheryl A. Woolhead, Peter J. McCormick, Arthur E. Johnson

Research output: Contribution to journalArticle

293 Citations (Scopus)

Abstract

Fluorescence resonance energy transfer measurements reveal that a transmembrane sequence within a nascent membrane protein folds into a compact conformation near the peptidyltransferase center and remains folded as the sequence moves through a membrane bound ribosome into the translocon. This compact conformation is compatible with an α helix because nearly the same energy transfer efficiency was observed when the transmembrane sequence was integrated into the lipid bilayer. Since the transmembrane sequence unfolds upon emerging from a free ribosome, this nascent chain folding is ribosome induced and stabilized. In contrast, a nascent secretory protein is in an extended conformation in the exit tunnel. Furthermore, two ribosomal proteins photocrosslink to nascent membrane but not secretory proteins. These interactions coincide with the previously described sequential closing and opening of the two ends of the aqueous translocon pore, thereby suggesting that ribosomal recognition of nascent chain folding controls the operational mode of the translocon at the ER membrane.
Original languageEnglish
Pages (from-to)725-736
Number of pages12
JournalCell
Volume116
Issue number5
DOIs
Publication statusPublished - 5 Mar 2004

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