Mannosidase activity of EDEM1 and EDEM2 depends on an unfolded state of their glycoprotein substrates

• Published in: Communications biology Vol. 1; no. 1; p. 172
• Main Authors: Shenkman, Marina, Ron, Efrat, Yehuda, Rivka, Benyair, Ron, Khalaila, Isam, Lederkremer, Gerardo Z.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2018; Nature Publishing Group
• Subjects: 13; 13/106; 631/80/221; 631/80/458/1524; 631/80/470/1463; 631/80/474/2287; 82; 82/16; 82/29; 82/80; Biology; Biomedical and Life Sciences; Endoplasmic reticulum; Glycoproteins; Life Sciences; Mannose; Mannosidase; N-glycans; Oligosaccharides; Polysaccharides; Protein disulfide-isomerase
• ISSN: 2399-3642; 2399-3642
• DOI: 10.1038/s42003-018-0174-8

Extensive mannose trimming of nascent glycoprotein N-glycans signals their targeting to endoplasmic reticulum-associated degradation (ERAD). ER mannosidase I (ERManI) and the EDEM protein family participate in this process. However, whether the EDEMs are truly mannosidases can be addressed only by measuring mannosidase activity in vitro. Here, we reveal EDEM1 and EDEM2 mannosidase activities in vitro. Whereas ERManI significantly trims free N-glycans, activity of the EDEMs is modest on free oligosaccharides and on glycoproteins. However, mannosidase activity of ERManI and the EDEMs is significantly higher on a denatured glycoprotein. The EDEMs associate with oxidoreductases, protein disulfide isomerase, and especially TXNDC11, enhancing mannosidase activity on glycoproteins but not on free N-glycans. The finding that substrate unfolded status increases mannosidase activity solves an important conundrum, as current models suggest general slow mannose trimming. As we show, misfolded or unfolded glycoproteins are subject to differentially faster trimming (and targeting to ERAD) than well-folded ones. Marina Shenkman et al. show that the ERAD mannosidases EDEM1 and EDEM2 have bona fide mannosidase activity in vitro. The activity of these enzymes is substantially faster when their glycoprotein substrates are in the unfolded state, suggesting a mechanism for efficient ERAD targeting of unfolded or misfolded glycoproteins.