Structural Studies and the Assembly of the Heptameric Post-translational Translocon Complex
In Saccharomyces cerevisiae, some of the nascent chains can be post-translationally translocated into the endoplasmic reticulum through the heptameric post-translational translocon complex (post-translocon). This membrane-protein complex is composed of the protein-conducting channel and the tetrameric Sec62/63 complex. The Sec62/63 complex plays crucial roles in targeting of the signal recognition particle-independent protein substrate to the protein-conducting channel and in assembly of the post-translocon. Although the molecular mechanism of the post-translational translocation process has been well established, the structure of the post-translocon and how the channel and the Sec62/63 complex form the heptameric complex are largely uncharacterized. Here, we report a 20-{angstrom} resolution cryo-electron microscopy structure of the post-translocon. The purified post-translocon was found to have a mass of 287 kDa, which is consistent with the unit stoichiometry of the seven subunits as determined by a cysteine labeling experiment. We demonstrated that Triton X-100 dissociated the heptameric complex into three subcomplexes identified as the trimeric translocon Sec61-Sbh1-Sss1, the Sec63-Sec71-Sec72 trimer, and the heterotetramer Sec62-Sec63-Sec71-Sec72, respectively. Additionally, a role of the sixth cytosolic loop of Sec61 in assembly of the post-translocon was demonstrated. Mutations of conserved, positively charged amino acid residues in the loop caused decreased formation of the post-translocon. These studies provide the first architectural description of the yeast post-translocon.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- LABORATORY-DIRECTED RESEARCH AND DEVELOPMENT
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1040561
- Report Number(s):
- BNL-94516-2011-JA; JBCHA3; R&D Project: 10-016; BO-108; YN0100000; TRN: US201210%%737
- Journal Information:
- Journal of Biological Chemistry, Vol. 286, Issue 4; ISSN 0021-9258
- Country of Publication:
- United States
- Language:
- English
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