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Related Concept Videos

Export of Misfolded Proteins out of the ER01:32

Export 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...
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Formation of Lipopolysaccharides

Lipopolysaccharides (LPS) are crucial components of the outer membrane of Gram-negative bacteria, serving both structural and functional roles. It contributes to membrane stability and protects bacteria from host immune responses. LPS is composed of three major regions—lipid A, a core oligosaccharide, and an O antigen. The biosynthesis and assembly of LPS involve a highly coordinated set of enzymatic reactions and transport mechanisms. Additionally, LPS is recognized as an endotoxin, triggering...
Inducible Operons: lac Operon01:25

Inducible Operons: lac Operon

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Related Experiment Video

Updated: Jun 26, 2026

Site-Specific Lysine Lactylation via Genetic Code Expansion in E. coli and Mammalian Cells
05:58

Site-Specific Lysine Lactylation via Genetic Code Expansion in E. coli and Mammalian Cells

Published on: February 24, 2026

Clogging the periplasmic pathway in LacY.

Yiling Nie1, Yonggang Zhou, H Ronald Kaback

  • 1Department of Physiology, Molecular Biology Institute, University of California, Los Angeles, California 90095, USA.

Biochemistry
|January 9, 2009
PubMed
Summary

Modifying the lactose permease (LacY) in Escherichia coli with bulky reagents in its periplasmic pathway blocks sugar transport. However, sugar binding to LacY remains unaffected, suggesting a crucial role for periplasmic pathway closure in transport.

Related Experiment Videos

Last Updated: Jun 26, 2026

Site-Specific Lysine Lactylation via Genetic Code Expansion in E. coli and Mammalian Cells
05:58

Site-Specific Lysine Lactylation via Genetic Code Expansion in E. coli and Mammalian Cells

Published on: February 24, 2026

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Membrane Transport

Background:

  • Lactose permease (LacY) in Escherichia coli is a dynamic membrane protein.
  • Crystal structures show LacY in an inward-facing conformation, with the binding site inaccessible from the periplasm.
  • Biochemical data suggest LacY undergoes conformational changes for transport, opening pathways to either side of the membrane alternately.

Purpose of the Study:

  • To investigate the relationship between the periplasmic pathway and LacY transport activity.
  • To determine the effect of modifying the periplasmic pathway on LacY function.

Main Methods:

  • Engineered single-Cys replacements in the periplasmic pathway of LacY.
  • Reaction of Cys replacements with thiol reagents of varying sizes.
  • Assay of LacY transport activity and sugar binding affinity.

Main Results:

  • Modification of periplasmic Cys residues with thiol reagents inactivated LacY-mediated transport.
  • Inactivation correlated with the size of the modifying reagent and the position of the Cys replacement.
  • Sugar binding to LacY was unaffected by the modifications.

Conclusions:

  • Placement of bulky moieties in the periplasmic cleft of LacY likely inhibits pathway closure, a critical step in the transport cycle.
  • These modifications do not significantly impede sugar access to the binding site.
  • Periplasmic pathway conformation is critical for LacY transport activity.