Name: how gram-negative bacteria export proteins
Uploaded: 2025-06-12T09:13:43.000Z
Duration: 1 min 17 s
Channel: JoVE

Gram-negative bacteria have one-step and two-step protein secretion systems for translocation into the outer lipopolysaccharide membrane or extracellular release.The one-step secretion systems, types I, III, IV, and VI, bypass the periplasm and form connected channels across both membranes.Type I systems transport substrates such as toxins directly out of the cell, while type III systems, often termed injectisomes, deliver effector proteins into host cells during infection.Type IV systems facilitate DNA transfer in horizontal gene transfer, while type VI systems use a phage-like contraction mechanism to inject toxins into competing bacteria or host cells.The two-step secretion systems, types II and V, depend on the Sec or Tat system to move proteins across the inner membrane.Type II secretion systems use a pseudopilus to push proteins, such as toxins and enzymes, from the periplasm across the outer membrane.Type V systems release proteins extracellularly or retain them in the outer membrane as adhesins.

gram-negative bacterial protein secretion systems

Gram-negative Bacterial Protein Secretion Systems

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:<ul><li>Type I Secretion System (T1SS): T1SS directly exports substrates, including toxins and proteases, from the cytoplasm to the extracellular environment. This system requires an ATP-binding cassette (ABC) transporter for energy-dependent translocation.</li><li>Type III Secretion System (T3SS): Also known as the injectisome, T3SS delivers effector proteins directly into host cells. These effectors modulate host cellular processes to benefit the bacteria, often playing critical roles in virulence during infection.</li><li>Type IV Secretion System (T4SS): T4SS facilitates the transfer of macromolecules, including DNA and proteins, during conjugation and horizontal gene transfer. Some pathogens also use it to inject virulence factors into host cells.</li><li>Type VI Secretion System (T6SS): T6SS employs a phage-like mechanism, using a contraction-based system to inject toxic effector proteins into competing bacteria or host cells. This system plays a role in bacterial competition and pathogenesis.</li></ul>Two-Step Secretion Systems (Types II and V)Two-step secretion systems rely on the Sec or Tat pathways to translocate proteins across the inner membrane into the periplasm. From there, additional components facilitate transport across the outer membrane:<ul><li>Type II Secretion System (T2SS): This system uses a pseudopilus, a dynamic pilus-like structure, to push proteins such as toxins and hydrolytic enzymes through a specialized pore in the outer membrane. These proteins often play roles in nutrient acquisition and pathogenesis.</li><li>Type V Secretion System (T5SS): Proteins secreted via this system carry an autotransporter domain that aids their translocation across the outer membrane. Some proteins are released extracellularly, while others remain anchored as adhesins, contributing to bacterial attachment and biofilm formation.</li></ul>

Gram-negative bacteria utilize sophisticated protein secretion systems to transport proteins across their double-membrane envelope into the extracellular ...

gram-negative-bacterial-protein-secretion-systems

Education

JoVE Core

Microbiology

Unit

Bacterial Genetics and Gene Regulation

KEY TERMS AND CONCEPTS

how gram-negative bacteria export proteins

Gram-negative bacteria use protein secretion systems to move proteins across their double-membrane envelope. These systems send proteins either into the extracellular environment or into host cells. They are grouped into one-step and two-step pathways based on how they move the proteins.

One-step secretion systems move proteins across both membranes in a single route. Type I secretion system (T1SS) exports substrates such as toxins and proteases directly from the cytoplasm outside the cell. It uses an ATP-binding cassette (ABC) transporter for energy-dependent movement. Type III secretion system (T3SS), also called the injectisome, sends effector proteins straight into host cells. These effectors change host cell processes and often support virulence during infection.

Type IV secretion system (T4SS) transfers macromolecules such as DNA and proteins during conjugation and horizontal gene transfer. Some pathogens also use T4SS to inject virulence factors into host cells. Type VI secretion system (T6SS) uses a phage-like, contraction-based mechanism. It injects toxic effector proteins into competing bacteria or host cells and helps with bacterial competition and pathogenesis.

Two-step secretion systems first use the Sec or Tat pathways to move proteins across the inner membrane into the periplasm. The periplasm is the space between the inner and outer membranes. From there, other parts of the system move the proteins across the outer membrane. Type II secretion system (T2SS) uses a pseudopilus, which is a dynamic pilus-like structure, to push proteins such as toxins and hydrolytic enzymes through a specialized outer-membrane pore. These proteins often help bacteria take up nutrients and cause disease.

Type V secretion system (T5SS) relies on an autotransporter domain to help proteins cross the outer membrane. Some of these proteins are released into the environment. Others stay attached to the cell as adhesins, which help bacteria attach and form biofilms.

How Gram-Negative Bacteria Export Proteins

how-gram-negative-bacteria-export-proteins

translation in prokaryotes

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bacterial translocation and protein secretion

bacterial-translocation-and-protein-secretion

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Gram-negative bacteria use protein secretion systems to move proteins across their double-membrane envelope. These systems send proteins either into the extracellular environment or into host cells. They are grouped into one-step and two-step pathways based on how they move the proteins. One-step secretion systems move proteins across both membranes in a single route. Type I secretion system (T1SS) exports substrates such as toxins and proteases directly from the cytoplasm outside the cell. It...

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other stress responses in bacteria

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horizontal gene transfer

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transformation

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conjugation

Bacterial DNA Transfer by Conjugation

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mechanism of conjugation

Bacterial Plasmid Transfer by Conjugation

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transduction

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development of antibiotic resistance

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key terms and concepts

Learn how gram-negative bacteria use one-step and two-step secretion systems to move toxins, enzymes, DNA, and effector proteins across their double membrane.

How Gram-Negative Bacteria Export Proteins | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

How Gram-Negative Bacteria Export Proteins

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