Abstract
Association of calnexin with newly synthesized glycoproteins involves recognition of monoglucosylated glycans, generated in the endoplasmic reticulum via initial removal of two glucose (Glc) residues from immature glycan chains by glucosidase enzymes (Glc trimming), or addition of a single Glc residue to fully trimmed glycans by glucosyltransferase enzymes (reglucosylation). While it has been established that creation of monoglucosylated glycans is important for chaperone binding, it is unknown if most proteins require both deglucosylation and reglucosylation for calnexin assembly or if initial Glc trimming is sufficient. Here, we studied the deglucosylation and reglucosylation of two related glycoproteins, the alpha and beta subunits of the T cell receptor (TCR) complex, and their assembly with calnexin in BW thymoma cells. Our data demonstrate that TCRalpha/beta glycoproteins undergo multiple cycles of Glc removal and addition within the endoplasmic reticulum and that numerous reglucosylated proteins assemble with calnexin, including TCRalpha/beta glycoproteins. Importantly, the current study shows that TCRbeta proteins, but not TCRalpha proteins, effectively associate with calnexin under conditions of functional Glc trimming but impaired reglucosylation. These data demonstrate that reglucosylated proteins associate with lectin-like chaperones in vivo and provide evidence that reglucosylation is of differential importance for the association of individual, indeed similar, glycoproteins with calnexin.
Highlights
This work is dedicated to Flora Ann Kirby Casteel. ‡ To whom correspondence should be addressed
Glucose:glycoprotein-dependent glucosyltransferase enzymes that transfer Glc residues to high mannose glycans on incompletely folded glycoproteins in the ER; and (iii) conversion of UDP-[3H]glucose into dolicholphospho-[3H]glucose, which is incorporated into nascent Glc3Man9GlcNAc2 glycans that are cotranslationally added to newly synthesized polypeptides in 3 min prior to radiolabeling; the presence of Chx and/or Cas was maintained during the radiolabeling procedure
The results in this study show that reglucosylated T cell antigen receptor (TCR)␣/ proteins and other unidentified reglucosylated proteins associate with calnexin in vivo, providing the first evidence that reglucosylated proteins interact with calnexin chaperones in intact cells of any type [15, 21]
Summary
Vol 272, No 7, Issue of February 14, pp. 4179 –4186, 1997 Printed in U.S.A. Reglucosylation of N-Linked Glycans Is Critical for Calnexin Assembly with T Cell Receptor (TCR) ␣ Proteins but Not TCR Proteins*. The current study shows that TCR proteins, but not TCR␣ proteins, effectively associate with calnexin under conditions of functional Glc trimming but impaired reglucosylation These data demonstrate that reglucosylated proteins associate with lectin-like chaperones in vivo and provide evidence that reglucosylation is of differential importance for the association of individual, similar, glycoproteins with calnexin. To further our understanding of the role of glycan processing and chaperone association in the quality control system of the ER, we studied the reglucosylation of TCR␣/ proteins and their assembly with calnexin in BW thymoma cells. These data demonstrate that TCR␣/ proteins undergo cycles of deglucosylation and reglucosylation in the ER and show that numerous reglucosylated proteins assemble with calnexin in intact cells, including TCR␣/ proteins. The results in the current study indicate that reglucosylation is critical for calnexin assembly with TCR␣ proteins but not TCR proteins
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
