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Biochim Biophys Acta Gen Subj. 2019 Sep;1863(9):1371-1380. doi: 10.1016/j.bbagen.2019.06.005. Epub 2019 Jun 10.

Proper insertion and topogenesis of membrane proteins in the ER depend on Sec63.

Author information

1
School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 08826, South Korea.
2
School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 08826, South Korea. Electronic address: joy@snu.ac.kr.

Abstract

BACKGROUND:

In eukaryotic cells, biogenesis of proteins destined to the secretory pathway begins from the cytosol. Nascent chains are either co-translationally or post-translationally targeted to the endoplasmic reticulum (ER) and translocated across the membrane through the Sec61 complex. For the post-translational translocation, the Sec62/Sec63 complex is additionally required. Sec63, however, is also shown to mediate co-translational translocation of a subset of proteins, the types and characteristics of proteins that Sec63 mediates in translocation still await to be defined.

METHODS:

To overview the types of proteins that require Sec63 for the ER translocation, we prepared Sec63 mutant lacking the first 39 residues (Sec63_ΔN39) in yeast and assessed initial translocation efficiencies of diverse types of precursors in the sec63_ΔN39 strain by a 5 min metabolic labeling. By employing Blue-Native gel electrophoresis (BN-PAGE), stability of the SEC complex (Sec61 plus Sec62/Sec63 complexes) isolated from cells carrying the Sec63_ΔN39 mutant was examined.

RESULTS:

Among the various translocation precursors tested, we found that proper sorting of single- and double-pass membrane proteins was severely impaired in addition to post-translational translocation precursor in the sec63_ΔN39 mutant strain. Stability of the SEC complex was compromised upon deletion of the N-terminal 39 residues.

CONCLUSIONS:

The N-terminus of Sec63 is important for stability of the SEC complex and Sec63 is required for proper sorting of membrane proteins in vivo.

GENERAL SIGNIFICANCE:

Sec63 is essential on insertion of membrane proteins.

KEYWORDS:

Endoplasmic reticulum (ER); Protein targeting; Protein translocation; Saccharomyces cerevisiae; Sec61; Sec62; Sec63; Signal sequence

PMID:
31195072
DOI:
10.1016/j.bbagen.2019.06.005
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