In vitro mannosidase activity of EDEM3 against asparagine-linked oligomannose-type glycans.

Oligomannose-type glycans on glycoproteins play an important role in the endoplasmic reticulum (ER)-protein quality control. Mannose trimming of the glycans triggers the ER-associated protein degradation pathway. In mammals, ER mannosyl-oligosaccharide 1,2-α-mannosidase 1 and three ER degradation -enhancing α-mannosidase-like proteins (EDEMs) are responsible for mannose trimming. However, the exact role of EDEMs as α-mannosidases in ERAD remains unclear. Here, we performed the biochemical characterization of EDEM3 using synthetic oligomannose-type glycan substrates. In vitro assays revealed that EDEM3 can convert an asparagine-linked M9 glycan to M8 and M7 glycans in contrast to glycine-linked M9 glycan, and the activity is enhanced in the presence of ERp46, a known partner protein of EDEM3. Our study provides novel insights into the enzymatic properties of EDEM3 and the use of artificial glycan substrates as tools to study ERAD mechanisms.