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Glycobiology Advance Access published online on June 9, 2004
Glycobiology, doi:10.1093/glycob/cwh110
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Received April 2, 2004
Revised June 3, 2004
Accepted June 4, 2004

ORIGINAL ARTICLES

Processing enzyme glucosidase II: proposed catalytic residues and developmental regulation during the ontogeny of the mouse mammary gland

Jie Feng 1, Andrew V. Romaniouk 1, Siba K. Samal 2, Inder K. Vijay 1*

1 Department of Animal and Avian Sciences, University of Maryland, College Park, MD 20742
2 Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, College Park, MD 20742

* To whom correspondence should be addressed. E-mail: ivijay{at}umd.edu.


  Abstract

Following the action of glucosidase I to clip the terminal {alpha}1,2-linked glucose, glucosidase II sequentially cleaves the two inner {alpha}1,3-linked glucose residues from the Glc{alpha}1,2Glc{alpha}1,3Glc{alpha}1,3Man9GlcNAc2 oligosaccharide of the incipient glycoprotein as it undergoes folding and maturation. Glucosidase II belongs to family 31 glycosidases. These enzymes act by the acid-base catalytic mechanism. The cDNA of the wild type and several mutant forms of the fusion protein of the enzyme in which mutations were introduced in the conserved motif, D564MNE567, were expressed in Sf9 cells and the proteins were purified on Ni-NTA matrix. The catalytic activity of the purified proteins was determined with radioactive Glc2Man9GlcNAc2 substrate. The results show that the aspartate and glutamate within the D564MNE567 motif can serve for catalysis, most likely as the acid-base pair within the active site of the enzyme.

The developmental regulation of glucosidase II was studied during the ontogeny of the mouse mammary gland for its growth and differentiation. The mRNA of both {alpha} and {beta} subunits of the enzyme, immunoreactive {alpha} and {beta} subunits and enzyme activity were measured over the complete developmental cycle. The changes in all the parameters were consistent with similar fluctuations with several other enzymes of the N-glycosylation machinery reported earlier, reaching a 3-4 fold increase over the basal level in the virgin gland at the peak of lactation. Taken together, it appears that there is a coordinated regulation of the enzymes involved in protein N-glycosylation during the development of the mouse mammary gland.

Key words: glucosidase II, active site, mammary gland


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