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Related Concept Videos

Protein Glycosylation01:25

Protein Glycosylation

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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...
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Oligosaccharide Assembly01:24

Oligosaccharide Assembly

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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...
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Proteoglycans01:05

Proteoglycans

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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,...
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Protein Modifications in the RER01:26

Protein Modifications in the RER

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Modification of secretory and transmembrane proteins entering the rough ER begins in the ER lumen. These modifications aid in protein folding and stabilize the acquired tertiary structure. Protein modifications in the rough ER co-occur at different stages of protein folding.
Broadly, these modifications can be categorized into four main categories — glycosylation, formation of disulfide bonds, assembly of protein subunits, and specific proteolytic cleavages like removal of signal...
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Protein Folding Quality Check in the RER01:29

Protein Folding Quality Check in the RER

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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...
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Conjugated Proteins02:50

Conjugated Proteins

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Simple proteins and protein complexes contain only amino acids. In contrast, many other proteins, called conjugated proteins, covalently bond with non-protein moieties.
Nucleoproteins are protein complexes that contain nucleic acids, categorized as deoxyribonucleoproteins (DNPs) or ribonucleoproteins (RNPs) respectively. The nucleosome is a typical example of a DNP where nuclear DNA is associated with histone proteins. The major antigen for the Covid-19 virus SARS-CoV is an RNP that is critical...
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Updated: Jun 15, 2025

Author Spotlight: Dendritic Cells Maturation Using Sialidases-Based Enzymatic Treatment of the Cell Surface
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Author Spotlight: Dendritic Cells Maturation Using Sialidases-Based Enzymatic Treatment of the Cell Surface

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Human apolipoprotein E glycosylation and sialylation: from structure to function.

Hee-Jung Moon1, Yan Luo1, Diksha Chugh1

  • 1Department of Pharmacology and Toxicology, School of Pharmacy, University of Kansas, Lawrence, KS, United States.

Frontiers in Molecular Neuroscience
|August 22, 2024
PubMed
Summary

Glycosylation, specifically sialylation, of human apolipoprotein E (ApoE) isoforms may explain their differing roles in Alzheimer's disease (AD) risk. ApoE2 is highly sialylated, offering neuroprotection, while ApoE4 is less sialylated, increasing AD risk.

Keywords:
Alzheimer’s diseaseapolipoprotein E (ApoE)glycosylationposttranslational modification (PTM)sialylation

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Metabolic Glycoengineering of Sialic Acid Using N-acyl-modified Mannosamines
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Metabolic Glycoengineering of Sialic Acid Using N-acyl-modified Mannosamines

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Optimized Negative Staining: a High-throughput Protocol for Examining Small and Asymmetric Protein Structure by Electron Microscopy
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Optimized Negative Staining: a High-throughput Protocol for Examining Small and Asymmetric Protein Structure by Electron Microscopy
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Optimized Negative Staining: a High-throughput Protocol for Examining Small and Asymmetric Protein Structure by Electron Microscopy

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Area of Science:

  • Neuroscience
  • Biochemistry
  • Genetics

Background:

  • Human apolipoprotein E (ApoE) isoforms (ApoE2, ApoE3, ApoE4) have distinct genetic associations with late-onset sporadic Alzheimer's disease (sAD).
  • ApoE4 confers the highest genetic risk for sAD, whereas ApoE2 provides neuroprotection.
  • The molecular basis for these opposing effects, despite minimal amino acid differences, remains a significant mystery.

Purpose of the Study:

  • To explore the hypothesis that post-translational sialoglycan modification of ApoE isoforms critically influences their distinct roles in sAD etiology.
  • To review current knowledge on ApoE glycosylation, particularly sialylation, in the brain and cerebrospinal fluid (CSF).
  • To present recent findings on differential sialylation of ApoE isoforms and its potential role in modulating amyloid-beta (Aβ) interactions and pathogenesis.

Main Methods:

  • Review of existing literature on ApoE structure, function, and post-translational modifications.
  • Analysis of species-, tissue-, and cell-specific glycosylation patterns of ApoE.
  • Examination of sialic acid modification (sialylation) in human ApoE from brain, CSF, and plasma.
  • Investigation of the relationship between ApoE sialylation levels and interaction with amyloid-beta (Aβ).

Main Results:

  • Human ApoE undergoes tissue-specific O-linked glycosylation, with significant sialylation observed in brain and CSF.
  • ApoE2 exhibits the highest degree of sialylation, ApoE4 the least, and ApoE3 intermediate levels.
  • Sialic acid moieties on ApoE may critically modulate ApoE's interaction with Aβ and subsequent Aβ pathogenesis.

Conclusions:

  • Differential sialylation of ApoE isoforms is a novel mechanism potentially explaining their opposing effects on sAD risk.
  • Sialylation of ApoE, particularly in the brain, may serve as a key modulator of Aβ pathology in Alzheimer's disease.
  • Further research into ApoE sialylation offers promising avenues for understanding sAD and developing therapeutic strategies.