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Related Concept Videos

Oligosaccharide Assembly01:24

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 RER01:29

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...
Coat Assembly and GTPases01:33

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Multi-pass Transmembrane Proteins and β-barrels01:09

Multi-pass Transmembrane Proteins and β-barrels

In multi-pass transmembrane proteins, the polypeptide chain crosses the membrane more than once. The transmembrane polypeptide chain either forms an α-helix or β-strand structure. α-Helix containing multi-pass transmembrane proteins are ubiquitous, whereas β-strand containing ones are mainly found in gram-negative bacteria, mitochondria, and chloroplasts.
α-Helix containing multi-pass transmembrane proteins
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Structure of Porins01:21

Structure of Porins

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Membrane Asymmetry Regulating Transporters01:19

Membrane Asymmetry Regulating Transporters

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Flippase
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Demonstration of Heterologous Complexes formed by Golgi-Resident Type III Membrane Proteins using Split Luciferase Complementation Assay
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The prototypical H+/galactose symporter GalP assembles into functional trimers.

Hongjin Zheng1, Justin Taraska, Alexey J Merz

  • 1Department of Biochemistry, University of Washington, 1705 NE Pacific Street, Seattle, WA 98195, USA.

Journal of Molecular Biology
|December 17, 2009
PubMed
Summary

Researchers reconstituted and crystallized galactose permease (GalP), a bacterial glucose transporter homolog. Structural analysis revealed GalP forms an active trimer, offering insights into sugar transport mechanisms.

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Last Updated: Jun 17, 2026

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Published on: December 9, 2020

Area of Science:

  • Biochemistry
  • Structural Biology
  • Membrane Transport

Background:

  • Glucose is a vital cellular energy source, transported by specialized membrane proteins.
  • Galactose permease (GalP) is a bacterial protein structurally homologous to human glucose transporters.

Purpose of the Study:

  • To functionally reconstitute and determine the 2D crystal structure of GalP.
  • To elucidate the oligomeric state and structural features of GalP relevant to its function.

Main Methods:

  • Single particle electron microscopy for structural analysis.
  • Functional reconstitution assays.
  • 2D crystallization and X-ray diffraction.

Main Results:

  • GalP was successfully reconstituted and formed 2D crystals in a hexagonal array with p3 symmetry.
  • Electron microscopy revealed GalP assembles into a trimer.
  • The projection structure at 18 Å resolution showed each monomer forming a channel, with an additional cavity at the 3-fold axis.
  • Crystalline GalP demonstrated selective substrate binding.

Conclusions:

  • The trimeric form of GalP is biologically active and capable of substrate binding.
  • Structural insights into the GalP trimer provide a model for human facilitated glucose transporters.