The function of Ensembl gene identifier ENSG00000177239 (MAN1B1, mannosidase alpha class 1B member 1) is as follows. Involved in glycoprotein quality control targeting of misfolded glycoproteins for degradation. It primarily trims a single alpha-1,2-linked mannose residue from Man(9)GlcNAc(2) to produce Man(8)GlcNAc(2), but at high enzyme concentrations, as found in the ER quality control compartment (ERQC), it further trims the carbohydrates to Man(5-6)GlcNAc(2). {ECO:0000269|PubMed:12090241, ECO:0000269|PubMed:18003979}.