A sweet code for glycoprotein folding

Glycoprotein synthesis is initiated in the endoplasmic reticulum (ER) lumen upon transfer of a glycan (Glc3Man9GlcNAc2) from a lipid derivative to Asn residues (N-glycosylation). N-Glycan-dependent quality control of glycoprotein folding in the ER prevents exit to Golgi of folding intermediates, irreparably misfolded glycoproteins and incompletely assembled multimeric complexes. It also enhances folding efficiency by preventing aggregation and facilitating formation of proper disulfide bonds. The control mechanism essentially involves four components, resident lectin-chaperones (calnexin and calreticulin) that recognize monoglucosylated polymannose protein-linked glycans, lectin-associated oxidoreductase acting on monoglucosylated glycoproteins (ERp57), a glucosyltransferase that creates monoglucosylated epitopes in protein-linked glycans (UGGT) and a glucosidase (GII) that removes the glucose units added by UGGT. This last enzyme is the only mechanism component sensing glycoprotein conformations as it creates monoglucosylated glycans exclusively in not properly folded glycoproteins or in not completely assembled multimeric glycoprotein complexes. Glycoproteins that fail to properly fold are eventually driven to proteasomal degradation in the cytosol following the ER-associated degradation pathway, in which the extent of N-glycan demannosylation by ER mannosidases play a relevant role in the identification of irreparably misfolded glycoproteins.Fil: Caramelo, Julio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Parodi, Armando José A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin

The Endoplasmic Reticulum Glucosyltransferase Recognizes Nearly Native Glycoprotein Folding Intermediates

The UDP-Glc:glycoprotein glucosyltransferase (GT), a key player in the endoplasmic reticulum (ER) quality control of glycoprotein folding, only glucosylates glycoproteins displaying non-native conformations. To determine whether GT recognizes folding intermediates or irreparably misfolded species with nearly native structures, we generated and tested as GT substrates neoglycoprotein fragments derived from chymotrypsin inhibitor 2 (GCI2) bearing from 53 to 64 (full-length) amino acids. Fragment conformations mimicked the last stage-folding structures adopted by a glycoprotein entering the ER lumen. GT catalytic efficiency (V(max)/K(m)) remained constant from GCI2-(1-53) to GCI2-(1-58) and then steadily declined to reach a minimal value with GCI2-(1-64). The same parameter showed a direct hyperbolic relationship with solvent accessibility of the single Trp residue but only in fragments exposing hydrophobic amino acid patches. Mutations introduced (GCI2-(1-63)V63S and GCI2-(1-64)V63S) produced slight structural destabilizations but increased GT catalytic efficiency. This parameter presented an inverse exponential relationship with the free energy of unfolding of canonical and mutant fragments. Moreover, the catalytic efficiency showed a linear relationship with the fraction of unfolded species in water. It was concluded that the GT-derived quality control may be operative with nearly native conformers and that no alternative ER-retaining mechanisms are required when glycoproteins approach their proper folding.Fil: Caramelo, Julio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Castro, Olga Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: de Prat Gay, Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Parodi, Armando José A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin

Action patterns of phosphorylase and glycogen synthetase on glycogen

originalFil: Parodi, Armando José A.. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Mordoh, Jose. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Krisman, Clara R.. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Leloir, Luis Federico. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaBlanco y negro9 páginas en pdfLFL-PI-O-ART. Artículos científicosUnidad documental simpleAR-HYL-201

In vitro synthesis of particulate glycogen from uridine diphosphate glucose

originalFil: Parodi, Armando José A.. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Mordoh, Jose. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Krisman, Clara R.. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Leloir, Luis Federico. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaBlanco y negro6 páginas en pdfLFL-PI-O-ART. Artículos científicosUnidad documental simpleAR-HYL-201

The role of dolichol monophosphate in sugar transfer

originalFil: Behrens, Nicolás H.. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Parodi, Armando José A.. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Leloir, Luis Federico. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaFil: Krisman, Clara R.. Instituto de Investigaciones Bioquímicas Fundación Campomar; ArgentinaBlanco y negro8 páginas en pdfLFL-PI-O-ART. Artículos científicosUnidad documental simpleAR-HYL-201

Analysis of Lipid-linked Oligosaccharides Synthesized in vivo in Schizosaccharomyces pombe

Dolichol diphosphate-linked oligosaccharides (LLO) are the sugar donors in N-glycosylation, a fundamental protein post-translational modification of the eukaryotic secretory pathway. Defects in LLO biosynthesis produce human Congenital Disorders of Glycosylation Type I. The synthesis of LLOs and the transfer reactions to their protein acceptors is highly conserved among animal, plant, and fungi kingdoms, making the fission yeast Schizosaccharomyces pombe a suitable model to study these processes. Here, we present a protocol to determine the LLO patterns produced in vivo by S. pombe cells that may be easily adapted to other cell types. First, exponentially growing cultures are labeled with a pulse of [14C]-glucose. LLOs are then purified by successive extractions with organic solvents, and glycans are separated from the lipid moieties in mild acid hydrolysis and a new solvent extraction. The purified glycans are then run on paper chromatography. We use a deconvolution process to adjust the profile obtained to the minimal number of Gaussian functions needed to fit the data and determine the proportion of each species with respect to total glycan species present in the cell. The method we provide here might be used without any expensive or specialized equipment. The deconvolution process described here might also be useful to analyze species in non-completely resolved chromatograms.Fil: Valko, Ayelén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, Biotecnología y Biología Traslacional; ArgentinaFil: Gallo, Giovanna Lucrecia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, Biotecnología y Biología Traslacional; Argentina. Ministerio de Producción y Trabajo. Secretaría de Gobierno de Agroindustria. Servicio Nacional de Sanidad y Calidad Agroalimentaria. Centro de Virología Humana y Animal. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Virología Humana y Animal; ArgentinaFil: Weisz, Ariel D.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, Biotecnología y Biología Traslacional; ArgentinaFil: Parodi, Armando José A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: D'alessio, Cecilia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, Biotecnología y Biología Traslacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Abrogation of glucosidase I–mediated glycoprotein deglucosylation results in a sick phenotype in fission yeasts: Model for the human MOGS-CDG disorder

Glucosidase I (GI) removes the outermost glucose from protein-linked Glc3Man9GlcNAc2 (G3M9) in the endoplasmic reticulum (ER). Individuals with congenital disorders of glycosylation MOGS-CDG bear mutations in the GI-encoding gene (gls1). Although GI absence has been reported to produce lethality in Schizosaccharomyces pombe yeasts, here we obtained two viable gls1 mutants, one with a very sick but not lethal phenotype (gls1-S) and the other with a healthier one (gls1-H). The sick strain displayed only G3M9 as an ER protein–linked oligosaccharide, whereas the healthier strain had both G3M9 and Man9GlcNAc2. The lipid-linked oligosaccharide patterns of the two strains revealed that the most abundantly formed glycans were G3M9 in gls1-S and Glc2Man9GlcNAc2 in gls1-H, suggesting reduced Alg10p glucosyltransferase activity in the gls1-H strain. A mutation in the alg10 gene was indeed observed in this strain. Our results indicated that abrogated G3M9 deglucosylation was responsible for the severe defects observed in gls1-S cells. Further studies disclosed that the defects could not be ascribed to disruption of glycoprotein entrance into calnexin-folding cycles, inhibition of the oligosaccharyltransferase by transfer reaction products, or reduced proteasomal degradation of misfolded glycoproteins. Lack of triglucosylated glycoprotein deglucosylation neither significantly prevented glycan elongation in the Golgi nor modified the overall cell wall monosaccharide composition. Nevertheless, it resulted in a distorted cell wall and in the absence of underlying ER membranes. Furthermore, Golgi expression of human endomannosidase partially restored normal growth in gls1-S cells. We propose that accumulation of G3M9-bearing glycoproteins is toxic and at least partially responsible for defects observed in MOGS-CDG.Fil: Gallo, Giovanna Lucrecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Valko, Ayelén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Aramburu, Sofía Ivana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Etchegaray Elcuaz, Emiliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Völker, Christof. Universitat Bonn; AlemaniaFil: Parodi, Armando José A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: D'Alessio, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin

Calreticulin and Calnexin as Chaperones in Glycoprotein Folding

Protein folding efficiency is enhanced in vivo by an array of chaperones and folding-assisting enzymes that cover the entire protein folding pathway, from the exit of the polypeptide from the ribosome, its translocation through membranes, disulfide bond formation, tertiary structure acquisition, and oligomer assembly. A protein acquires diverse conformational states during these processes, from extended and disordered structures when exiting the ribosome to more structured intermediates such as molten globule-like forms. Accordingly, the high diversity of chaperones reflects the conformational variety of their substrates. From a statistical point of view, the native state represents an extremely small fraction of the conformational space available to a protein, which may easily fall into irreversible kinetic traps during the folding process. In this sense, the crowded environment inside a cell represents a hostile scenario for protein folding, where protein aggregation could be the rule rather than the exception. One of the main functions of chaperones, perhaps the most important, is to inhibit nonspecific protein interactions, directing the protein to a productive folding pathway.Fil: Caramelo, Julio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Parodi, Armando José A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin

Glycoprotein Folding and Processing Reactions

The N-glycan-dependent quality control of glycoprotein folding occurring in the endoplasmic reticulum prevents exit to Golgi of folding intermediates, irreparably misfolded glycoproteins, and incompletely assembled multimeric complexes. It also enhances folding efficiency by preventing aggregation and facilitating formation of proper disulfide bonds. The control mechanism essentially involves four components, two resident lectin-chaperones, calnexin and calreticulin, that recognize monoglucosylated polymannose protein-linked glycans, a lectin-associated oxidoreductase acting on monoglucosylated glycoproteins, a glucosyltransferase that creates monoglucosytlated epitopes in protein-linked glycans, and a glucosidase that removes the glucose units added by the glucosyltransferase. The glucosyltransferase is the only mechanism component sensing glycoprotein conformations as it creates monoglucosylated glycans exclusively in not properly folded species or in not completely assembled complexes. The glucosidase is a heterodimer composed of a catalytic subunit and an additional one that is responsible for the ER localization of the enzyme. The glucosyltransferase, the glucosidase, and calreticulin, but not calnexin, are soluble proteins.Fil: Caramelo, Julio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Parodi, Armando José A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin

Quality Control in Glycoprotein Folding

The concept of quality control of protein folding in the secretory pathway emerged in the late 1970s and early 1980s when it was noticed that not in all cases did insertion of proteins in the endoplasmic reticulum (ER) result in their appearance at the expected final destination, intra- or extracellular. Several experimental results showed that cells displayed mechanisms that ensured that only proteins in their native conformations could be produced by the secretory pathway. Those mechanisms received the collective denomination of ‘‘quality control’’. Protein folding in living cells is a complex, error-prone process. Numerous mechanisms are in place to ensure that newly synthesized proteins reach their folded functional form. One such mechanism is the addition of glycans occurring in the ER lumen. Covalently linked N-glycans affect protein folding in cell-free assays, as they provide bulky, highly hydrophilic substituents that maintain molecules in solution while protein moieties successively adopt a variety of different conformations before reaching their final structures. In addition, the highly hydrophilic nature of N-glycans forces the asparagine units to which they are linked and neighboring amino acids to be in or close to the water-protein interphase. This chapter will not deal with those effects, which certainly also occur in vivo, but with folding-efficiency enhancement and ER retention of folding intermediates and irreparably misfolded species mediated by the interaction of a specific glycan structure (monoglucosylated polymannose-type compounds) with the ER lectins calnexin (CNX) and calreticulin (CRT). Recent evidence suggesting a role for a specific putative lectin (EDEM/Htm1p/Man1p) on the disposal of irreparably misfolded glycoproteins will be discussed also.Fil: Trombetta, E. Sergio. Yale Medical School; Estados UnidosFil: Parodi, Armando José A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin