Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum

Newly synthesized glycoproteins interact during folding and quality control in the ER with calnexin and calreticulin, two lectins specific for monoglucosylated oligosaccharides. Binding and release are regulated by two enzymes, glucosidase II and UDP-Glc:glycoprotein:glycosyltransferase (GT), which...

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Main Authors:	Trombetta, E. Sergio, Helenius, Ari
Format:	Online
Language:	English
Published:	The Rockefeller University Press 2000
Online Access:	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2174309/

id	pubmed-2174309
recordtype	oai_dc
spelling	pubmed-21743092008-05-01 Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum Trombetta, E. Sergio Helenius, Ari Brief Report Newly synthesized glycoproteins interact during folding and quality control in the ER with calnexin and calreticulin, two lectins specific for monoglucosylated oligosaccharides. Binding and release are regulated by two enzymes, glucosidase II and UDP-Glc:glycoprotein:glycosyltransferase (GT), which cyclically remove and reattach the essential glucose residues on the N-linked oligosaccharides. GT acts as a folding sensor in the cycle, selectively reglucosylating incompletely folded glycoproteins and promoting binding of its substrates to the lectins. To investigate how nonnative protein conformations are recognized and directed to this unique chaperone system, we analyzed the interaction of GT with a series of model substrates with well defined conformations derived from RNaseB. We found that conformations with slight perturbations were not reglucosylated by GT. In contrast, a partially structured nonnative form was efficiently recognized by the enzyme. When this form was converted back to a nativelike state, concomitant loss of recognition by GT occurred, reproducing the reglucosylation conditions observed in vivo with isolated components. Moreover, fully unfolded conformers were poorly recognized. The results indicated that GT is able to distinguish between different nonnative conformations with a distinct preference for partially structured conformers. The findings suggest that discrete populations of nonnative conformations are selectively reglucosylated to participate in the calnexin/calreticulin chaperone pathway. The Rockefeller University Press 2000-03-20 /pmc/articles/PMC2174309/ /pubmed/10725325 Text en © 2000 The Rockefeller University Press This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).
repository_type	Open Access Journal
institution_category	Foreign Institution
institution	US National Center for Biotechnology Information
building	NCBI PubMed
collection	Online Access
language	English
format	Online
author	Trombetta, E. Sergio Helenius, Ari
spellingShingle	Trombetta, E. Sergio Helenius, Ari Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum
author_facet	Trombetta, E. Sergio Helenius, Ari
author_sort	Trombetta, E. Sergio
title	Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum
title_short	Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum
title_full	Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum
title_fullStr	Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum
title_full_unstemmed	Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum
title_sort	conformational requirements for glycoprotein reglucosylation in the endoplasmic reticulum
description	Newly synthesized glycoproteins interact during folding and quality control in the ER with calnexin and calreticulin, two lectins specific for monoglucosylated oligosaccharides. Binding and release are regulated by two enzymes, glucosidase II and UDP-Glc:glycoprotein:glycosyltransferase (GT), which cyclically remove and reattach the essential glucose residues on the N-linked oligosaccharides. GT acts as a folding sensor in the cycle, selectively reglucosylating incompletely folded glycoproteins and promoting binding of its substrates to the lectins. To investigate how nonnative protein conformations are recognized and directed to this unique chaperone system, we analyzed the interaction of GT with a series of model substrates with well defined conformations derived from RNaseB. We found that conformations with slight perturbations were not reglucosylated by GT. In contrast, a partially structured nonnative form was efficiently recognized by the enzyme. When this form was converted back to a nativelike state, concomitant loss of recognition by GT occurred, reproducing the reglucosylation conditions observed in vivo with isolated components. Moreover, fully unfolded conformers were poorly recognized. The results indicated that GT is able to distinguish between different nonnative conformations with a distinct preference for partially structured conformers. The findings suggest that discrete populations of nonnative conformations are selectively reglucosylated to participate in the calnexin/calreticulin chaperone pathway.
publisher	The Rockefeller University Press
publishDate	2000
url	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2174309/
_version_	1611425570626732032

Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum

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