Both isoforms of human UDP-glucose:glycoprotein glucosyltransferase are enzymatically active

Abstract

Being recognized as an important constituent of the glycoprotein folding cycle, uridine diphosphate-glucose:glycoprotein glucosyltransferase (UGGT) has been a subject of intense study. Up to now, it is two isoforms, UGGT1 and 2 have been identified, which share ∼ 50% amino acid identity. UGGT1 is a well-documented enzyme which functions as a folding sensor in the endoplasmic reticulum, by the virtue of its ability to transfer a glucose residue to non-glucosylated high-mannose-type glycans of immature glycoproteins exhibiting non-native conformation. On the other hand, direct evidence to support the glucosyltransferase activity of UGGT2 has been lacking, leaving it unclear as to whether it has any function in the glycoprotein folding process. This study aimed to reveal the property of human UGGT2 by using synthetic substrates such as fluorescently labeled glycans and N-glycosylated proteins. The analysis, for the first time, revealed the glucosyltransferase activity of UGGT2, whose specificity was shown to be quite similar to UGGT1, in terms of both glycan specificity and preferential recognition of proteins having non-native conformations. Finally, Sep15 was found to form the heterodimeric complex with both isoforms of UGGT and markedly enhanced its glucosyltransferase activity.

N-linked sugar-regulated protein folding and quality control in the ER

“…It was originally proposed that UGT2 lacks re-glucosylation activity (131) yet, a recent study showed that UGT2 has re-glucosylation activity and similar specificity to UGT1. This study used a cell free re-glucosylation assay (132). Further investigations are required to confirm the function of UGT2.…”

The relationship between glycan structures and expression levels of an endoplasmic reticulum-resident glycoprotein, UDP-glucose: Glycoprotein glucosyltransferase 1

“…The plasmids were transfected into 293T cells using Lipofectamine 2000 (Life Technologies Japan, Tokyo, Japan) according to the manufacturer's instructions. After 48 h, the cells were harvested and the recombinant proteins were purified using Anti-FLAG M2-agarose (SigmaeAldrich Japan, Tokyo, Japan) as described previously [22].…”

Single-particle electron microscopy structure of UDP-glucose:glycoprotein glucosyltransferase suggests a selectivity mechanism for misfolded proteins

“…It is a large monomeric protein of more than 1500 residues and found in almost all eukaryotes. The activity of UGGT has been probed using native and misfolded glycoproteins (7, 10 -13), glycopeptides (14 -16), and small synthetic substrates (17)(18)(19)(20)(21)(22). These studies have shown a strong selectivity for glucosylation of misfolded over folded substrates.…”