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Journal Article

Cotranslational protein targeting to the membrane: Nascent-chain transfer in a quaternary complex formed at the translocon.

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Draycheva,  A.
Department of Physical Biochemistry, MPI for biophysical chemistry, Max Planck Society;

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Lee,  S.
Department of Physical Biochemistry, MPI for biophysical chemistry, Max Planck Society;

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Wintermeyer,  W.
Research Group of Ribosome Dynamics, MPI for biophysical chemistry, Max Planck Society;

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2616209.pdf
(Publisher version), 4MB

Supplementary Material (public)

2616209_Suppl.docx
(Supplementary material), 3MB

Citation

Draycheva, A., Lee, S., & Wintermeyer, W. (2018). Cotranslational protein targeting to the membrane: Nascent-chain transfer in a quaternary complex formed at the translocon. Scientific Reports, 8(1): 9922. doi:10.1038/s41598-018-28262-8.


Cite as: http://hdl.handle.net/21.11116/0000-0001-A46B-E
Abstract
Membrane proteins in bacteria are cotranslationally inserted into the plasma membrane through the SecYEG translocon. Ribosomes exposing the signal-anchor sequence (SAS) of a membrane protein are targeted to the translocon by the signal recognition particle (SRP) pathway. SRP scans translating ribosomes and forms high-affinity targeting complexes with those exposing a SAS. Recognition of the SAS activates SRP for binding to its receptor, FtsY, which, in turn, is primed for SRP binding by complex formation with SecYEG, resulting in a quaternary targeting complex. Here we examine the effect of SecYEG docking to ribosome-nascent-chain complexes (RNCs) on SRP binding and SAS transfer, using SecYEG embedded in phospholipid-containing nanodiscs and monitoring FRET between fluorescence-labeled constituents of the targeting complex. SecYEG-FtsY binding to RNC-SRP complexes lowers the affinity of SRP to both ribosome and FtsY, indicating a general weakening of the complex due to partial binding competition near the ribosomal peptide exit. The rearrangement of the quaternary targeting complex to the pre-transfer complex requires an at least partially exposed SAS. The presence of SecYEG-bound FtsY and the length of the nascent chain strongly influence nascent-chain transfer from SRP to the translocon and repositioning of SRP in the post-transfer complex.