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Related Concept Videos

Operons02:09

Operons

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Prokaryotes can control gene expression through operons—DNA sequences consisting of regulatory elements and clustered, functionally related protein-coding genes. Operons use a single promoter sequence to initiate transcription of a gene cluster (i.e., a group of structural genes) into a single mRNA molecule. The terminator sequence ends transcription. An operator sequence, located between the promoter and structural genes, prohibits the operon’s transcriptional activity if bound by...
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Inducible Operons: lac Operon01:25

Inducible Operons: lac Operon

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The lac operon in Escherichia coli is a model for understanding inducible gene regulation and metabolic flexibility. It integrates local control by lactose and global regulation through catabolite repression, enabling E. coli to preferentially metabolize glucose when available and switch to lactose utilization when glucose is scarce.Structure and Function of the lac OperonThe lac operon contains three structural genes: lacZ (β-galactosidase), lacY (lactose permease), and lacA...
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Bacterial Translocation and Protein Secretion01:26

Bacterial Translocation and Protein Secretion

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Bacterial protein secretion involves translocation systems to ensure proteins reach their designated locations, including the plasma membrane, periplasm, outer membrane, or the external environment. These translocation systems are vital for bacterial physiology, supporting processes like membrane assembly, enzymatic activity in the periplasm, and interactions with the external environment. The division of labor between Sec and Tat pathways ensures efficiency in handling proteins with diverse...
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Gram-negative Bacterial Protein Secretion Systems01:17

Gram-negative Bacterial Protein Secretion Systems

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Gram-negative bacteria utilize sophisticated protein secretion systems to transport proteins across their double-membrane envelope into the extracellular environment or host cells. Based on their mechanism of action, these systems are classified into one-step and two-step pathways.One-Step Secretion Systems (Types I, III, IV, and VI)One-step secretion systems bypass the periplasm entirely, forming a continuous channel that spans both the inner and outer membranes:Type I Secretion System (T1SS):...
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Formation of Lipopolysaccharides01:19

Formation of Lipopolysaccharides

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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,...
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Coordination of Gene Expression Processes in Bacteria01:29

Coordination of Gene Expression Processes in Bacteria

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The DNA replication, transcription, and translation processes are intricately coupled in bacteria, allowing efficient gene expression and rapid protein synthesis. While this physical and functional coordination is advantageous, it introduces challenges that bacteria overcome through specific regulatory mechanisms.Coupling of Replication, Transcription, and TranslationThe coupling of replication, transcription, and translation is a hallmark of bacterial gene expression. As the replisome unwinds...
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Related Experiment Video

Updated: Apr 15, 2026

Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli
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Membrane protein expression in Lactococcus lactis.

Martin S King1, Christoph Boes1, Edmund R S Kunji1

  • 1The Medical Research Council, Mitochondrial Biology Unit, Cambridge, United Kingdom.

Methods in Enzymology
|April 11, 2015
PubMed
Summary
This summary is machine-generated.

Lactococcus lactis is an excellent host for producing functional membrane proteins due to its rapid growth and controlled gene expression. This bacterium facilitates efficient protein production and purification for research applications.

Keywords:
ChannelFunctional expressionMembrane vesiclesMitochondrial carriersNisin-inducible expression systemReceptorTransporter

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Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles
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Area of Science:

  • Microbiology
  • Molecular Biology
  • Biotechnology

Background:

  • Lactococcus lactis is a Gram-positive bacterium with advantageous characteristics for protein overproduction.
  • Its rapid growth, high cell density capacity, and lack of aeration requirement support large-scale fermentation.
  • Tight regulation of strong promoter systems enables controlled expression of potentially toxic gene products.

Purpose of the Study:

  • To detail protocols for expressing membrane proteins in L. lactis.
  • To highlight the suitability of L. lactis as a host for functional membrane protein production.
  • To cover the process from gene cloning to membrane vesicle isolation for expression analysis.

Main Methods:

  • Utilizing L. lactis for rapid, high-density fermentation without aeration.
  • Employing tightly regulated promoter systems for controlled gene expression.
  • Targeting expressed proteins to the cytoplasmic membrane for in-cell studies.
  • Leveraging the organism's genetic features for complementation and purification.
  • Using mild detergents for protein solubilization and amino acid auxotrophy for labeling.

Main Results:

  • L. lactis facilitates the overproduction of membrane proteins in a functional form.
  • Expressed proteins are exclusively targeted to the cytoplasmic membrane, enabling functional studies.
  • Stable plasmids and reproducible expression levels are achieved.
  • Proteins are often stable due to limited proteolytic activity and easily solubilized.
  • Complementation studies and purification are simplified by the small genome size.

Conclusions:

  • Lactococcus lactis offers a robust and versatile platform for the functional overproduction of membrane proteins.
  • The described protocols provide a comprehensive guide for harnessing L. lactis in membrane protein research.
  • Despite minor challenges like low transformation frequency, L. lactis remains a highly effective host for biotechnological applications.