Cloning and expression of a specific human alpha 1,2-mannosidase that trims Man9GlcNAc2 to Man8GlcNAc2 isomer B during N-glycan biosynthesis

Glycobiology. 1999 Oct;9(10):1073-8. doi: 10.1093/glycob/9.10.1073.


We report the isolation of a novel human cDNA encoding a type II membrane protein of 79.5 kDa with amino acid sequence similarity to Class I alpha 1,2-mannosidases. The catalytic domain of the enzyme was expressed as a secreted protein in Pichia pastoris. The recombinant enzyme removes a single mannose residue from Man9GlcNAc and [1H]-NMR analysis indicates that the only product is Man8GlcNAc isomer B, the form lacking the middle-arm terminal alpha 1,2-mannose. Calcium is required for enzyme activity and both 1-deoxymannojirimycin and kifunensine inhibit the human alpha 1,2-mannosidase. The properties and specificity of this human alpha 1,2-mannosidase are identical to the endoplasmic reticulum alpha 1,2-mannosidase from Saccharomyces cerevisiae and differ from those of previously cloned Golgi alpha 1,2-mannosidases that remove up to four mannose residues from Man9GlcNAc2 during N-glycan maturation. Northern blot analysis showed that all human tissues examined express variable amounts of a 3 kb transcript. This highly specific alpha 1,2-mannosidase is likely to be involved in glycoprotein quality control since there is increasing evidence that trimming of Man9GlcNAc2 to Man8GlcNAc2 isomer B in yeast cells is important to target misfolded glycoproteins for degradation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Carbohydrate Sequence
  • Cloning, Molecular
  • DNA Primers / genetics
  • DNA, Complementary / genetics
  • Gene Expression
  • Humans
  • Magnetic Resonance Spectroscopy
  • Mannosidases / genetics*
  • Mannosidases / metabolism*
  • Molecular Sequence Data
  • Oligosaccharides / chemistry
  • Oligosaccharides / metabolism
  • Pichia / genetics
  • Polysaccharides / biosynthesis*
  • Polysaccharides / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Substrate Specificity


  • DNA Primers
  • DNA, Complementary
  • Oligosaccharides
  • Polysaccharides
  • Recombinant Proteins
  • Mannosidases
  • mannosyl-oligosaccharide 1,2-alpha-mannosidase

Associated data

  • GENBANK/AF148509