Related Experiment Video
Updated: Jul 11, 2026
10:17
Pulse-chase Analysis of N-linked Sugar Chains from Glycoproteins in Mammalian Cells
Published on: April 28, 2010
Glycoprotein biosynthesis. Rat liver microsomal glucosidases which process oligosaccharides
The Journal of Biological Chemistry
|September 25, 1979
Summary
Researchers identified two distinct membrane-bound glucosidases in rat liver microsomes. These enzymes are crucial for the initial steps in glycoprotein post-translational modification, specifically removing glucose residues from asparagine-linked oligosaccharides.
Area of Science:
- Biochemistry
- Cell Biology
- Glycobiology
Background:
- Asparagine-linked oligosaccharides on glycoproteins undergo significant processing after protein attachment.
- A critical stage in this post-glycosylation modification involves the stepwise elimination of glucose units from the oligosaccharide.
- Understanding these enzymatic activities is key to deciphering cellular glycoprotein maturation.
Purpose of the Study:
- To investigate the glucosidase activities involved in glycoprotein processing in rat liver.
- To characterize the enzymes responsible for glucose removal from specific oligosaccharide precursors.
- To elucidate the localization and potential biological significance of these glucosidases.
Main Methods:
- Utilized rat liver microsomes to study glucose removal from Glc3Man9GlcNAc, Glc2Man9GlcNAc, and Glc1Man9GlcNAc.
- Employed detergent solubilization, inhibitor studies, and temperature-activity profiles to differentiate enzymatic activities.
- Solubilized and purified one of the identified glucosidases 12-fold.
Main Results:
- Evidence suggests the presence of at least two distinct membrane-bound glucosidases.
- One glucosidase acts on Glc3Man9GlcNAc, removing the terminal glucose residue.
- A second glucosidase sequentially processes Glc2Man9GlcNAc and Glc1Man9GlcNAc, with this enzyme being purified.
- These integral membrane proteins are located on the cisternal surface of rough and smooth microsomes.
Conclusions:
- Rat liver microsomes contain distinct glucosidases essential for early glycoprotein processing.
- These enzymes initiate the removal of glucose residues from N-linked oligosaccharides.
- The localization and activity of these glucosidases highlight their biological importance in glycoprotein maturation.
Related Concept Videos
01:25Protein Glycosylation
Glycosylation, the most common post-translational modification for proteins, serves diverse functions. Adding sugars to proteins makes the proteins more resistant to proteolytic digestion. Glycosylated proteins can act as markers and receptors to promote cell-cell adhesion. Additionally, they have many essential quality control functions in the cell, such as correct protein folding and facilitating transport of misfolded proteins to the cytosol, which can be degraded.
Glycosylation occurs in...
Glycosylation occurs in...
01:24Oligosaccharide Assembly
Protein glycosylation starts in the ER lumen and continues in the Golgi apparatus. Glycosyltransferases catalyze the addition of sugar molecules or glycosylation of proteins. Usually, these enzymes add sugars to the hydroxyl groups of selected serine or threonine residues to form O-linked glycans or the amino groups of asparagine residues to form N-linked glycans. Different positions on the same polypeptide chain can contain differently linked glycans.
Multiple sugar molecules that may or may...
Multiple sugar molecules that may or may...
01:29Protein Folding Quality Check in the RER
ER is the primary site for the maturation and folding of soluble and transmembrane secretory proteins. The calnexin cycle is a specific chaperone system that folds and assesses the confirmation of N-glycosylated proteins before they can exit the ER lumen. The primary players of this quality check pipeline are the lectins, ER-resident chaperones, and a glucosyl transferase enzyme. In case the calnexin system in the lumen fails to salvage a misfolded protein, it is transported to the cytoplasm...
01:32Export of Misfolded Proteins out of the ER
After folding, the ER assesses the quality of secretory and membrane proteins. The correctly folded proteins are cleared by the calnexin cycle for transport to their final destination, while misfolded proteins are held back in the ER lumen. The ER chaperones attempt to unfold and refold the misfolded proteins but sometimes fail to achieve the correct native conformation. Such terminally misfolded proteins are then exported to the cytosol by ER-associated degradation or ERAD pathway for...
01:05Proteoglycans
Glycans, a class of complex heterogeneous molecules, can be covalently attached to proteins to form glycosylated proteins that regulate various physiological and pathological processes. Glycosylated proteins or glycoproteins comprise N-linked and O-linked oligosaccharides. O-glycosylation is the most common type of protein glycosylation. Here, glycans attach to the oxygen atom of the hydroxyl groups of Serine or Threonine residues. O-linked glycosylation occurs later in protein processing,...
01:26Biosynthesis of Polysaccharides
Polysaccharides such as glycogen and starch are synthesized from nucleoside diphosphate sugars, primarily uridine diphosphate glucose (UDPG) and adenosine diphosphate glucose (ADPG). These activated glucose donors act as key intermediates in carbohydrate metabolism and biosynthesis. UDPG primarily involves glycogen synthesis in animals and many bacteria, while ADPG plays a fundamental role in starch synthesis in plants and certain bacteria.UDPG is formed when glucose-1-phosphate reacts with...