Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published March 31, 2015 | Supplemental Material + Published
Journal Article Open

Ribosome–SRP–FtsY cotranslational targeting complex in the closed state


The signal recognition particle (SRP)-dependent pathway is essential for correct targeting of proteins to the membrane and subsequent insertion in the membrane or secretion. In Escherichia coli, the SRP and its receptor FtsY bind to ribosome–nascent chain complexes with signal sequences and undergo a series of distinct conformational changes, which ensures accurate timing and fidelity of protein targeting. Initial recruitment of the SRP receptor FtsY to the SRP–RNC complex results in GTP-independent binding of the SRP–FtsY GTPases at the SRP RNA tetraloop. In the presence of GTP, a closed state is adopted by the SRP–FtsY complex. The cryo-EM structure of the closed state reveals an ordered SRP RNA and SRP M domain with a signal sequence-bound. Van der Waals interactions between the finger loop and ribosomal protein L24 lead to a constricted signal sequence-binding pocket possibly preventing premature release of the signal sequence. Conserved M-domain residues contact ribosomal RNA helices 24 and 59. The SRP–FtsY GTPases are detached from the RNA tetraloop and flexible, thus liberating the ribosomal exit site for binding of the translocation machinery.

Additional Information

© 2015 National Academy of Sciences. Edited by Joachim Frank, Howard Hughes Medical Institute, Columbia University, New York, NY, and approved February 20, 2015 (received for review December 30, 2014). Published online before print March 16, 2015, doi: 10.1073/pnas.1424453112 . We thank Sejeong Lee and Wolfgang Wintermeyer (Max Planck Institute for Biophysical Chemistry, Göttingen, Germany) for discussions and information about Lep50; Wim Hagen for data collection; the protein expression facility at EMBL Heidelberg and the Partnership for Structural Biology in Grenoble for support; and all members of C.S.'s group for discussion and advice with image processing. The Polara microscope is part of the Institut de Biologie Structurale Structural Biology and Dynamics GIS-IBISA–labeled platform. Support was provided by ERC Starting Grant Project 281331 (to C.S.). Author contributions: O.v.L., S.-o.S., and C.S. designed research; O.v.L., Q.J., A.A., M.K., and K.H. performed research; O.v.L., Q.J., A.A., M.K., and C.S. analyzed data; and O.v.L., Q.J., I.B., S.-o.S., and C.S. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. Data deposition: The EM maps and atomic models have been deposited in the Protein Data Bank, www.pdb.org (PDB ID code 5AKA), and EMDataBank, www.emdatabank.org (accession no. EMD-2917). This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1424453112/-/DCSupplemental.

Attached Files

Published - 3943.full.pdf

Supplemental Material - pnas.1424453112.sapp.pdf


Files (11.9 MB)
Name Size Download all
10.6 MB Preview Download
1.3 MB Preview Download

Additional details

August 22, 2023
October 20, 2023