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Oligosaccharide Assembly

Oligosaccharide 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...

Protein Folding Quality Check in the RER

Protein 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...

Protein Glycosylation

Protein 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...

Glucose Transporters

Glucose Transporters

Glucose transporters facilitate the transport of glucose across the cell membrane. In addition to glucose, some glucose transporters can also aid the movement of other hexoses such as fructose, mannose, and galactose.
Facilitated diffusion-glucose transporters (GLUTs) are encoded by the solute-linked carrier (SLC) family 2, subfamily A gene family, or SLC2A. The 14 GLUT protein members are distributed into three classes:

Proteoglycans

Proteoglycans

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,...

Tail-anchoring of Proteins in the ER Membrane

Tail-anchoring of Proteins in the ER Membrane

Tail-anchored, or TA, proteins are estimated to make up to 3-5% of membrane proteins found in the eukaryotic cell. Such proteins have a single transmembrane domain located approximately 30 amino acid residues upstream from the C-terminal end. As a result, the signal recognition particle (SRP) cannot guide a TA protein to the ER membrane for cotranslational insertion. Hence, they are integrated into the ER membrane post-translationally using their C-terminal end as the anchor. TA proteins...

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Related Experiment Video

Updated: Jul 6, 2026

Generation of Null Mutants to Elucidate the Role of Bacterial Glycosyltransferases in Bacterial Motility

Generation of Null Mutants to Elucidate the Role of Bacterial Glycosyltransferases in Bacterial Motility

Published on: March 11, 2022

Structure and function of beta -1,4-galactosyltransferase.

Pradman K Qasba¹, Boopathy Ramakrishnan, Elizabeth Boeggeman

¹Structural Glycobiology Section, CCRNP, NCI-Frederick, Building 469, Room 221, Frederick, Maryland 21702, USA. qasba@helix.nih.gov

Current Drug Targets

|April 9, 2008

Summary

Beta-1,4-galactosyltransferase (beta4Gal-T1) is a key enzyme in glycoconjugate synthesis. Its conformational changes enable substrate binding and product release, and its interaction with alpha-lactalbumin facilitates lactose synthesis.

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Generation of Null Mutants to Elucidate the Role of Bacterial Glycosyltransferases in Bacterial Motility

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Demonstration of Heterologous Complexes formed by Golgi-Resident Type III Membrane Proteins using Split Luciferase Complementation Assay

Published on: September 10, 2020

Area of Science:

Biochemistry
Glycobiology
Molecular Biology

Background:

Beta-1,4-galactosyltransferase (beta4Gal-T1) is a trans-Golgi enzyme essential for synthesizing the Galbeta1-4-GlcNAc disaccharide in glycoconjugates.
It possesses a type II membrane protein topology with distinct cytoplasmic, membrane-spanning, stem, and catalytic domains.

Purpose of the Study:

To elucidate the structure-function relationship of beta4Gal-T1, focusing on its catalytic domain and conformational dynamics.
To understand the mechanism of substrate binding, product transfer, and the role of alpha-lactalbumin in modulating enzyme activity.

Main Methods:

Analysis of the catalytic domain structure, including flexible loops and metal/sugar-nucleotide binding sites.
Investigation of conformational changes upon substrate binding using structural and biochemical approaches.
Study of the interaction between beta4Gal-T1 and alpha-lactalbumin.

Main Results:

Beta4Gal-T1's catalytic domain features two flexible loops that undergo significant conformational changes upon metal ion and sugar-nucleotide binding.
These conformational changes create transient oligosaccharide acceptor and donor binding sites, facilitating the glycosylation reaction.
Alpha-lactalbumin binding induces a conformational change that alters beta4Gal-T1's acceptor specificity, enabling lactose synthesis.

Conclusions:

The conformational flexibility of beta4Gal-T1's catalytic loops is crucial for its enzymatic activity and regulation.
Understanding these mechanisms allows for the engineering of novel glycosyltransferases with tailored specificities for synthesizing complex carbohydrates and inhibitors.