Glucosylation of glycoproteins in Crithidia fasciculata

Götz, G.; Gañan, Sandra A.; Parodi, Armando J.

doi:10.1016/0166-6851(91)90094-m

Cited by 15 publications

(8 citation statements)

References 17 publications

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“…Trypanosomatid protozoa also express a GII activity able to remove glucose units from monoglucosylated oligosaccharides created by GT (Bosch et al, 1988). Concentrations of inhibitors (DNJ and castanospermine) required for attaining 50% inhibition of trypanosomatid GII were similar (if not identical) to values reported for the mammalian enzyme, thus suggesting a high similarity between GII activities from both origins Gotz et al, 1991).…”

Section: Discussionmentioning

confidence: 50%

Trypanosoma cruziCalreticulin Is a Lectin That Binds Monoglucosylated Oligosaccharides but Not Protein Moieties of Glycoproteins

Labriola

Cazzulo

Parodi³

1999

MBoC

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Trypanosoma cruzi is a protozoan parasite that belongs to an early branch in evolution. Although it lacks several features of the pathway of protein N-glycosylation and oligosaccharide processing present in the endoplasmic reticulum of higher eukaryotes, it displays UDP-Glc:glycoprotein glucosyltransferase and glucosidase II activities. It is herewith reported that this protozoan also expresses a calreticulin-like molecule, the third component of the quality control of glycoprotein folding. No calnexin-encoding gene was detected. Recombinant T. cruzi calreticulin specifically recognized free monoglucosylated high-mannose-type oligosaccharides. Addition of anti-calreticulin serum to extracts obtained from cells pulse-chased with [35 S]Met plus [35 S]Cys immunoprecipitated two proteins that were identified as calreticulin and the lysosomal proteinase cruzipain (a major soluble glycoprotein). The latter but not the former protein disappeared from immunoprecipitates upon chasing cells. Contrary to what happens in mammalian cells, addition of the glucosidase II inhibitor 1-deoxynojirimycin promoted calreticulin-cruzipain interaction. This result is consistent with the known pathway of protein N-glycosylation and oligosaccharide processing occurring in T. cruzi. A treatment of the calreticulin-cruzipain complexes with endo-␤-N-acetylglucosaminidase H either before or after addition of anti-calreticulin serum completely disrupted calreticulincruzipain interaction. In addition, mature monoglucosylated but not unglucosylated cruzipain isolated from lysosomes was found to interact with recombinant calreticulin. It was concluded that the quality control of glycoprotein folding appeared early in evolution, and that T. cruzi calreticulin binds monoglucosylated oligosaccharides but not the protein moiety of cruzipain. Furthermore, evidence is presented indicating that glucosyltransferase glucosylated cruzipain at its last folding stages.

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Section: Discussionmentioning

confidence: 50%

Trypanosoma cruziCalreticulin Is a Lectin That Binds Monoglucosylated Oligosaccharides but Not Protein Moieties of Glycoproteins

Labriola

Cazzulo

Parodi³

1999

MBoC

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“…Reglucosylation of incompletely folded glycoproteins in the ER mediates their interaction with calnexin, calreticulin, and ERp57, which are part of a unique glycoproteinspecific chaperone system. Most glycoproteins are reglucosylated during their biogenesis (Gañan et al, 1991;Gotz et al, 1991), and several glycoproteins have been specifically shown to be reglucosylated in vivo during their maturation in the ER, including vesicular stomatitis G protein (Cannon and Helenuis, 1999;Suh et al, 1989), influenza HA (Hebert et al, 1995), transferrin (Wada et al, 1997), T cell receptor subunits (Van Leeuwen and Kearse, 1997), and cruzipain (Labriola et al, 1999). The reglucosylating enzyme uses only nonnative glycoproteins as substrates in vitro (Sousa et al, 1992;Trombetta and Parodi, 1992;Fernandez et al, 1994;Parker et al, 1995), recognizing occupied glycosylation sites covalently attached to nonnative protein backbones (Sousa et al, 1992;Trombetta and Parodi, 1992;Fernandez et al, 1994;Parker et al, 1995;Sousa and Parodi, 1995).…”

Section: Discussionmentioning

confidence: 99%

Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum

Trombetta

Helenius

2000

The Journal of Cell Biology

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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.

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“…The glucosyltransferase is a soluble, ubiquitously expressed, resident ER enzyme composed of two identical 150-kDa subunits (Parodi et al, 1984;Ganan et al, 1991;Gotz et al, 1991;Trombetta et al, 1991;Sousa et al, 1992;Trombetta and Parodi, 1992). It catalyzes the posttranslational reglucosylation of protein-linked highmannose oligosaccharides.…”

Section: Misfolded Glycoproteins Undergo De-and Reglucosylation In Thmentioning

confidence: 99%

How N-linked oligosaccharides affect glycoprotein folding in the endoplasmic reticulum.

Helenius

1994

MBoC

609

480

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Glucosylation of glycoproteins in Crithidia fasciculata

Cited by 15 publications

References 17 publications

Trypanosoma cruziCalreticulin Is a Lectin That Binds Monoglucosylated Oligosaccharides but Not Protein Moieties of Glycoproteins

Trypanosoma cruziCalreticulin Is a Lectin That Binds Monoglucosylated Oligosaccharides but Not Protein Moieties of Glycoproteins

Conformational Requirements for Glycoprotein Reglucosylation in the Endoplasmic Reticulum

How N-linked oligosaccharides affect glycoprotein folding in the endoplasmic reticulum.

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