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Structural Insight into How Bacteria Prevent Interference between Multiple Divergent Type IV Secretion Systems.

Joseph J Gillespie1, Isabelle Q H Phan2, Holger Scheib3

  • 1Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA JGillespie@som.umaryland.edu arto.pulliainen@utu.fi.

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Summary
This summary is machine-generated.

Bacteria use multiple type IV secretion systems (T4SSs) for essential functions. This study reveals structural and regulatory mechanisms, like differential expression and component diversification, that prevent T4SSs from interfering with each other.

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Area of Science:

  • Microbiology and Molecular Biology
  • Bacterial Pathogenesis
  • Structural Biology

Background:

  • Prokaryotes utilize type IV secretion systems (T4SSs) for translocating diverse substrates and forming surface structures.
  • Some bacteria, like Bartonella and Rickettsia, possess multiple, functionally distinct T4SSs, posing challenges for maintaining system independence.
  • Understanding the evolutionary and functional implications of component interchangeability among multiple T4SSs within a single bacterium is crucial.

Purpose of the Study:

  • To investigate the structural and regulatory factors governing the maintenance of multiple, analogous T4SSs within a single bacterial cell.
  • To elucidate the mechanisms preventing cross-system interchangeability of T4SS components in bacteria.
  • To identify potential drug targets by understanding the unique barriers that maintain the functional independence of bacterial T4SSs.

Main Methods:

  • Determined crystal structures of VirB8 and TrwG proteins from Bartonella species.
  • Employed bacterial two-hybrid assays and molecular modeling to analyze protein-protein interactions.
  • Determined the crystal structure of Rickettsia typhi RvhB8-II and modeled its paralog RvhB8-I.

Main Results:

  • VirB8 and TrwG proteins exhibit conserved structural folds and dimerization interfaces despite significant sequence divergence, indicating strong structural constraints.
  • Differential expression of Bartonella vir and trw systems acts as a barrier to VirB8-TrwG interchangeability.
  • Rickettsia rvh T4SS displays divergent VirB8 paralogs (RvhB8-I and RvhB8-II) with distinct dimerization interfaces, suggesting functional diversification and preventing heterodimerization.

Conclusions:

  • Bacteria employ distinct strategies, including spatiotemporal regulation (Bartonella) and structural diversification (Rickettsia), to maintain the functional independence of multiple T4SSs.
  • These findings highlight the intricate regulation required for managing multiple analogous protein complexes within a single organism.
  • Targeting the regulatory barriers of T4SSs could offer a novel therapeutic strategy against bacterial infections, as these systems lack eukaryotic homologs.