Structural basis for catalysis and inhibition of N-glycan processing class I alpha 1,2-mannosidases

J Biol Chem. 2000 Dec 29;275(52):41287-98. doi: 10.1074/jbc.M006927200.


Endoplasmic reticulum (ER) class I alpha1,2-mannosidase (also known as ER alpha-mannosidase I) is a critical enzyme in the maturation of N-linked oligosaccharides and ER-associated degradation. Trimming of a single mannose residue acts as a signal to target misfolded glycoproteins for degradation by the proteasome. Crystal structures of the catalytic domain of human ER class I alpha1,2-mannosidase have been determined both in the presence and absence of the potent inhibitors kifunensine and 1-deoxymannojirimycin. Both inhibitors bind to the protein at the bottom of the active-site cavity, with the essential calcium ion coordinating the O-2' and O-3' hydroxyls and stabilizing the six-membered rings of both inhibitors in a (1)C(4) conformation. This is the first direct evidence of the role of the calcium ion. The lack of major conformational changes upon inhibitor binding and structural comparisons with the yeast alpha1, 2-mannosidase enzyme-product complex suggest that this class of inverting enzymes has a novel catalytic mechanism. The structures also provide insight into the specificity of this class of enzymes and provide a blueprint for the future design of novel inhibitors that prevent degradation of misfolded proteins in genetic diseases.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 1-Deoxynojirimycin / chemistry
  • 1-Deoxynojirimycin / metabolism
  • Alkaloids / chemistry
  • Alkaloids / metabolism
  • Amino Acid Sequence
  • Animals
  • Calcium / metabolism
  • Catalysis
  • Endoplasmic Reticulum / enzymology*
  • Humans
  • Mannosidases / antagonists & inhibitors*
  • Molecular Sequence Data
  • Polysaccharides / metabolism
  • Protein Conformation
  • Rabbits
  • Recombinant Proteins / isolation & purification
  • Structure-Activity Relationship


  • Alkaloids
  • Polysaccharides
  • Recombinant Proteins
  • kifunensine
  • 1-Deoxynojirimycin
  • Mannosidases
  • mannosyl-oligosaccharide 1,2-alpha-mannosidase
  • Calcium

Associated data

  • PDB/1FM1
  • PDB/1FO2
  • PDB/AFO3