Involved in endoplasmic reticulum-associated degradation (ERAD). Accelerates the glycoprotein ERAD by proteasomes, by catalyzing mannose trimming from Man8GlcNAc2 to Man7GlcNAc2 in the N-glycans . May also participate in mannose trimming from all glycoproteins and not just misfolded ones targeted to ERAD . May have alpha 1,2-mannosidase activity (By similarity).
Subcellular locations: Endoplasmic reticulum lumen