UDP-glucose: glycoprotein glucosyltransferase
(UGGT) is a 170 kDa lumenal endoplasmic reticulum (ER) resident
protein that catalyzes monoglucosylation of high mannose oligosaccharides.
UGGT catalyzes the transfer of glucose from UDP-glucose to Man7-9GlcNAc2-moiety
of unfolded glycoproteins in a Ca2+ dependent reaction. UGGT binds
unfolded glycoprotein via two elements on its substrate: a N-acetylglucosamine
unit on the oligosaccharide and hydrophobic amino acids that are
exposed in the denatured conformation. It is postulated that UGGT
serves as a sensor that is able to distinguish between folded and
denatured protein in the ER.
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