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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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Secretory vesicles, also known as dense core vesicles (DCVs), are membrane-bound vesicles that transport secretory proteins, such as hormones or neurotransmitters. Regulated secretory vesicles transport proteins from the trans-Golgi network to the exterior of the cell. Proteins present in regulated secretory vesicles are required to be rapidly exocytosed in large amounts upon a specific stimulus.
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Pathogenic bacteria employ a range of regulatory mechanisms to modulate the expression of virulence genes in response to environmental and host-derived signals. These mechanisms ensure that virulence factors are expressed only under favorable conditions, thereby optimizing infection and survival strategies.Mechanisms of Virulence RegulationKey regulatory strategies include:Two-Component Systems: These consist of a membrane-bound sensor kinase and a cytoplasmic response regulator. Environmental...
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Bacterial conjugation is a mechanism of horizontal gene transfer that enables the exchange of genetic material between bacterial cells through direct contact. This process is facilitated by a donor cell carrying a conjugative plasmid, which encodes genes necessary for pilus formation, DNA replication, and transfer. The conjugative plasmid plays a central role in initiating and executing the transfer of genetic material.The tra region of the conjugative plasmid encodes proteins responsible for...
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Exocrine glands are those that release their secretions through ducts. Based on their mode of secretion, they can be classified into merocrine, apocrine, and holocrine.
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Type VII Secretion: A Highly Versatile Secretion System.

Louis S Ates1, Edith N G Houben2, Wilbert Bitter1,2

  • 1Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.

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Type VII secretion (T7S) systems are crucial for bacteria like mycobacteria to export proteins across their cell envelope. This review details T7S components, substrates, and roles in virulence, particularly in pathogenic bacteria.

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Area of Science:

  • Microbiology
  • Cell Biology
  • Protein Secretion

Background:

  • Type VII secretion (T7S) systems enable mycobacteria and other bacteria to secrete proteins across complex cell envelopes.
  • T7S systems are widespread in Actinobacteria and also found in Firmicutes, secreting diverse protein families like Esx, PE, and PPE.
  • Pathogenic mycobacteria utilize multiple T7S systems (ESX-1 to ESX-5) for distinct roles in physiology and virulence.

Purpose of the Study:

  • To provide a comprehensive overview of the general composition and function of T7S systems.
  • To elucidate the roles of conserved T7S components, including ATPase (EccC) and protease (MycP).
  • To discuss the function of intracellular chaperones in T7S substrate recognition and explore system-specific variations.

Main Methods:

  • Review of existing literature on T7S systems in mycobacteria and other bacteria.
  • Analysis of conserved T7S components and their predicted enzymatic activities.
  • Integration of recent crystal structure and molecular analyses of T7S components and substrates.

Main Results:

  • T7S systems secrete folded heterodimeric substrates, a conserved feature across different bacterial phyla.
  • Key conserved components include EccC (ATPase for energy) and MycP (subtilisin-like protease for substrate processing).
  • A conserved intracellular chaperone plays a role in recognizing T7S substrates.

Conclusions:

  • T7S systems are essential for the secretion of diverse substrates, including virulence factors, across the diderm cell envelope.
  • Understanding T7S mechanisms and components is critical for deciphering bacterial pathogenesis and developing novel therapeutic strategies.
  • System-specific features of T7S contribute to the unique pathogenic potential of different bacterial species.