Involved in the endoplasmic reticulum-associated degradation (ERAD) pathway that targets misfolded glycoproteins for degradation in an N-glycan-dependent manner (PubMed:15579471, PubMed:25655076). May initiate ERAD by promoting the first mannose trimming step of ERAD substrates, from Man9GlcNAc2 to Man8GlcNAc2 (By similarity). Seems to recognize and bind to exposed hydrophobic regions in target proteins (PubMed:25655076). Up-regulated by the unfolded protein response (UPR) via the XBP1 transcription factor. N-glycosylated. Belongs to the glycosyl hydrolase 47 family. Has similarity to alpha 1,2-mannosidases, but the catalytic activity of this protein is controversial. One study shows that it is important for a specific oligosaccharide trimming step from Man9GlcNAc2 to Man8GlcNAc2, suggesting activity as a mannosidase. However, another study reports that this protein has no mannosidase activity.