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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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Fimbriae and pili are specialized bacterial surface structures that play pivotal roles in adhesion, genetic exchange, and motility. Composed primarily of pilin protein, these hairlike appendages are crucial for bacterial survival and pathogenicity in various environments.Fimbriae: Adhesion and PathogenicityFimbriae are fine, filamentous structures measuring 2–10 nanometers in diameter and are densely distributed on the bacterial cell surface. They facilitate bacterial adhesion to abiotic...
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Mechanism of Conjugation01:19

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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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Bacterial Translocation and Protein Secretion01:26

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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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Mechanism of Filopodia Formation01:39

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Filopodia are thin, actin-rich cellular protrusions that play an important role in many fundamental cellular functions. They vary in their occurrence, length, and positioning in different cell types, suggesting their diverse roles.
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Conjugative Mating Assays for Sequence-specific Analysis of Transfer Proteins Involved in Bacterial Conjugation
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Type IV secretion systems: Advances in structure, function, and activation.

Tiago R D Costa1, Laith Harb2, Pratick Khara3

  • 1MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London, UK.

Molecular Microbiology
|December 16, 2020
PubMed
Summary
This summary is machine-generated.

Bacterial type IV secretion systems (T4SSs) are diverse molecular machines. Recent advances reveal their assembly, architecture, and function, offering insights into DNA transfer and effector delivery mechanisms.

Keywords:
conjugationcryoelectron microscopycryoelectron tomographyeffector translocationpilus

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Structural Biology

Background:

  • Bacterial type IV secretion systems (T4SSs) are crucial for microbial interactions, mediating DNA transfer and effector delivery.
  • T4SSs are classified into conjugation and effector translocator subfamilies, with variations in Gram-positive and Gram-negative bacteria.
  • Both 'minimized' and 'expanded' T4SSs utilize conserved core subunits, with expanded systems incorporating additional specific components.

Purpose of the Study:

  • To review recent advancements in understanding the structure-function relationships of bacterial type IV secretion systems (T4SSs).
  • To highlight progress in defining the assembly pathways and architectures of model Gram-negative T4SSs.
  • To explore how structural insights address fundamental questions about T4SS mechanisms and versatility.

Main Methods:

  • Utilizing fluorescence microscopy to visualize T4SS assembly and dynamics.
  • Employing cryo-electron microscopy for high-resolution structural determination of T4SS components and complexes.
  • Integrating structural data with functional studies of model T4SSs.

Main Results:

  • Detailed architectures of both minimized (e.g., Agrobacterium tumefaciens VirB/VirD4) and expanded (e.g., Helicobacter pylori Cag, Legionella pneumophila Dot/Icm, F plasmid Tra) T4SSs have been elucidated.
  • Atomic-resolution insights have been gained into key processes such as substrate recruitment, channel formation, and pilus assembly.
  • Adaptations in T4SS machinery contributing to their diverse functional capabilities have been identified.

Conclusions:

  • Recent structural and assembly studies provide unprecedented insights into the molecular mechanisms of bacterial type IV secretion systems.
  • Understanding T4SS structure-function relationships is key to deciphering their roles in bacterial pathogenesis and evolution.
  • Continued investigation of model T4SSs promises to resolve long-standing questions and reveal novel aspects of macromolecule transport in bacteria.