Molecular Biology of the Cell

Home Help [Feedback] [For Subscribers] [Archive] [Search] --
QUICK SEARCH:   [advanced]


     

MBC in Press, published online ahead of print November 19, 2008
Mol. Biol. Cell 10.1091/mbc.E08-09-0902

This Article
Right arrow Full Text (PDF)
Right arrow Supplemental Materials
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Google Scholar
Right arrow Articles by Pitonzo, D.
Right arrow Articles by Skach, W. R.
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pitonzo, D.
Right arrow Articles by Skach, W. R.

Submitted on September 3, 2008
Accepted on November 12, 2008

Sequence-Specific Retention and Regulated Integration of a Nascent Membrane Protein by the ER Sec61 Translocon

David Pitonzo,* Zhongying Yang,* Yoshihiro Matsumura, Arthur E. Johnson,{dagger}{ddagger} and William R. Skach*

*Department of Biochemistry and Molecular Biology, Oregon Health and Sciences University, Portland, OR 97239; {dagger}Department of Molecular and Cellular Medicine, Texas A&M University System Health Science Center, College Station, TX 77843-1114; {ddagger}Departments of Chemistry, and Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843

Monitoring Editor: Peter Walter

A defining feature of eukaryotic polytopic protein biogenesis involves integration, folding and packing of hydrophobic transmembrane segments (TMs) into the apolar environment of the lipid bilayer. In the endoplasmic reticulum, this process is facilitated by the Sec61 translocon. Here we use a photocrosslinking approach to examine integration intermediates derived from the ABC transporter CFTR and show that the timing of translocon-mediated integration can be regulated at specific stages of synthesis. During CFTR biogenesis, the eighth TM segment exits the ribosome and enters the translocon in close proximity to Sec61{alpha}. This interaction is initially weak, and TM8 spontaneously dissociates from the translocon when the nascent chain is released from the ribosome. Polypeptide extension by only a few residues, however, results in stable TM8-Sec61{alpha} photocrosslinks that persist after peptidyl-tRNA bond cleavage. Retention of these untethered polypeptides within the translocon requires ribosome binding and is mediated by an acidic residue, Asp924, near the center of the putative TM8 helix. Remarkably, at this stage of synthesis, nascent chain release from the translocon is also strongly inhibited by ATP depletion. These findings contrast with passive partitioning models and indicate that Sec61{alpha} can retain TMs and actively inhibit membrane integration in a sequence-specific and ATP dependent manner.

Address correspondence to: William R. Skach (skachw{at}ohsu.edu)






Home Help [Feedback] [For Subscribers] [Archive] [Search] --
Copyright © 2008 by The American Society for Cell Biology. Terms of copyright protection, warranties, and disclaimers.