Fusion of an intact secretory protein permits a misfolded protein to exit from the endoplasmic reticulum in yeast

Abstract

Upon exit from the endoplasmic reticulum (ER), the nascent polypeptides of secretory proteins undergo sorting events. If properly folded, they are directly or indirectly recognized by the coat proteins of budding vesicles for forward transport, while unfolded or misfolded proteins are retained in the ER by a quality control mechanism. To gain insight into the interplay between ER export and ER quality control, we fused a secretory protein invertase to the C-terminus of mutated carboxypeptidase Y (CPY*), a model ER-associated degradation (ERAD) substrate in Saccharomyces cerevisiae. This substrate, designated CPY*-Inv, was largely exported from the ER, although it was fully recognized by the ERAD-related lectin, Yos9, and hence degraded by the ERAD when it remained in the ER. CPY*-Inv relied primarily on the p24 complex, a putative ER export receptor for invertase, for escape from ERAD, suggesting that the ERAD and the ER export of soluble secretory proteins are competitive.

Graphical Abstract

In the endoplasmic reticulum (ER), ERAD machineries and export receptors compete secretory proteins to determine whether they are degraded or exported from the ER.

Key words:

• misfolded protein
• endoplasmic reticulum (ER)-associated degradation
• carboxypeptidase Y
• invertase
• yeast

Acknowledgments

We thank Dr. Davis T. Ng and Dr. Shuh-Ichi Nishikawa for providing plasmids, and antibodies.

Funding

This work was supported by MEXT KAKENHI [grant number 17780249], [grant number 20059002]; JSPS KAKENHI [grant number 19580391].

Notes

Abbreviations: ER, endoplasmic reticulum; COPII, coat protein complex II; ERAF, ER-assisted folding; ERAD, ER-associated degradation; FoldEx, folding for export; CPY, carboxypeptidase Y; CHX, cycloheximide; Endo H, endoglycosidase H; PGK, 3-phosphoglycerate kinase; HIP, Hrd1-independent proteolysis; VPS, vacuolar protein sorting.