Mannosidase Alpha Class 1B Member 1 (MAN1B1)

The deduced 699-amino acid protein contains a cytoplasmic tail and a putative transmembrane domain. Northern blot analysis detected a 3-kb MAN1B1 transcript at variable levels in all tissues examined, with particularly high expression in testis and relatively low expression in lung and muscle. The full-length cDNA predicts a 663-amino acid protein with a molecular mass of 76,002 Da and a sequence characteristic of type II transmembrane polypeptides. Northern blot analysis detected a 2.8-kb transcript in all tissues examined. Substrate specificity and inhibitor sensitivity of a recombinant protein derived from the cDNA and expressed in COS cells indicated that the cDNA encodes the ER mannosidase I enzyme. Immunolocalization of epitope-tagged ER mannosidase I showed colocalization with ER marker proteins.