Endoplasmic reticulum-associated degradation of misfolded glycoproteins ensures only functional, correctly folded proteins exit from the endoplasmic reticulum and that misfolded ones are targeted for lysosomal degradation. Misfolded glycoproteins are deglycosylated in the cytosol and the resultant free oligosaccharide can be further hydrolysed by alpha-mannosidase 2C1 (MAN2C1). For example, the oligosaccharide structure GlcNAc (Man)9 is hydrolysed by MAN2C1 to GlcNAc (Man)5, an intermediate structure formed in the N-glycan precursor biosynthesis pathway (Suzuki et al. 2006).
alpha-mannosidase activity of MAN2C1:Zn2+ [cytosol]