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Two alternative binding mechanisms connect the protein translocation Sec71-Sec72 complex with heat shock proteins

Journal Article · · Journal of Biological Chemistry
 [1];  [2];  [2];  [1]
  1. Harvard Medical School, Boston, MA (United States). Howard Hughes Medical Inst. Dept. of Cell Biology
  2. Univ. of Massachusetts Medical School, Worcester, MA (United States). Dept. of Biochemistry and Molecular Pharmacology
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The biosynthesis of many eukaryotic proteins requires accurate targeting to and translocation across the endoplasmic reticulum membrane. Post-translational protein translocation in yeast requires both the Sec61 translocation channel, and a complex of four additional proteins: Sec63, Sec62, Sec71, and Sec72. The structure and function of these proteins are largely unknown. This pathway also requires the cytosolic Hsp70 protein Ssa1, but whether Ssa1 associates with the translocation machinery to target protein substrates to the membrane is unclear. Here, we use a combined structural and biochemical approach to explore the role of Sec71-Sec72 subcomplex in post-translational protein translocation. To this end, we report a crystal structure of the Sec71-Sec72 complex, which revealed that Sec72 contains a tetratricopeptide repeat (TPR) domain that is anchored to the endoplasmic reticulum membrane by Sec71. We also determined the crystal structure of this TPR domain with a C-terminal peptide derived from Ssa1, which suggests how Sec72 interacts with full-length Ssa1. Surprisingly, Ssb1, a cytoplasmic Hsp70 that binds ribosome-associated nascent polypeptide chains, also binds to the TPR domain of Sec72, even though it lacks the TPR-binding C-terminal residues of Ssa1. We demonstrate that Ssb1 binds through its ATPase domain to the TPR domain, an interaction that leads to inhibition of nucleotide exchange. Taken together, our results suggest that translocation substrates can be recruited to the Sec71-Sec72 complex either post-translationally through Ssa1 or co-translationally through Ssb1.
Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Organization:
USDOE Office of Science (SC)
OSTI ID:
1372257
Journal Information:
Journal of Biological Chemistry, Journal Name: Journal of Biological Chemistry Journal Issue: 19 Vol. 292; ISSN 0021-9258
Publisher:
American Society for Biochemistry and Molecular BiologyCopyright Statement
Country of Publication:
United States
Language:
ENGLISH

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Cited By (11)

Post-Translational Protein Transport by the Sec Complex journal June 2019
MANF antagonizes nucleotide exchange by the endoplasmic reticulum chaperone BiP text January 2019
MANF antagonizes nucleotide exchange by the endoplasmic reticulum chaperone BiP journal February 2019
Structure of the post-translational protein translocation machinery of the ER membrane journal December 2018
Binding properties of the quaternary assembly protein SPAG1 journal June 2019
Conserved motifs on the cytoplasmic face of the protein translocation channel are critical for the transition between resting and active conformations journal August 2018
Guiding tail-anchored membrane proteins to the endoplasmic reticulum in a chaperone cascade journal October 2019
Structure of the posttranslational Sec protein-translocation channel complex from yeast journal December 2018
Targeting and translocation of proteins to the endoplasmic reticulum at a glance journal December 2017
A clearer picture of the ER translocon complex journal February 2020
Substrate relay in an Hsp70‐cochaperone cascade safeguards tail‐anchored membrane protein targeting journal July 2018

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
70 kilodalton heat shock protein (Hsp70)
Sec71
Sec72
Ssa1
Ssb1
TPR
endoplasmic reticulum (ER)
protein structure
protein translocation
structure-function