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Lateral opening and exit pore formation are required for BamA function.

Nicholas Noinaj1, Adam J Kuszak1, Curtis Balusek2

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Summary
This summary is machine-generated.

The bacterial outer membrane protein assembly machinery (Bam) complex, specifically BamA, facilitates outer membrane protein insertion. New findings reveal BamA requires lateral opening and a substrate exit pore for its essential function in protein biogenesis.

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Area of Science:

  • Microbiology
  • Structural Biology
  • Biochemistry

Background:

  • Gram-negative bacteria possess an outer membrane containing essential beta-barrel outer membrane proteins (OMPs).
  • The biogenesis and insertion of OMPs into the outer membrane are critical for bacterial survival and function.
  • The precise mechanism of OMP folding and membrane insertion, particularly the role of the beta-barrel assembly machinery (Bam) complex, remains largely unelucidated.

Purpose of the Study:

  • To investigate the structural and functional mechanism of BamA, a key component of the Bam complex.
  • To elucidate the role of BamA's lateral opening and potential substrate exit pathways in OMP biogenesis.

Main Methods:

  • Molecular dynamics (MD) simulations were employed to study BamA structure and dynamics.
  • Disulfide crosslinking experiments were performed to probe the functional relevance of structural features.
  • Biochemical rescue experiments using tris(2-carboxyethyl)phosphine were conducted.

Main Results:

  • MD simulations revealed a substrate exit pore in BamA, located above the lateral opening site.
  • Disulfide crosslinks preventing lateral opening and exit pore formation abolished BamA function.
  • The loss of BamA function due to crosslinking was fully rescued by a reducing agent.

Conclusions:

  • Lateral opening of the BamA barrel domain and the formation of a substrate exit pore are essential for BamA function.
  • These findings provide strong evidence for a specific mechanism of OMP insertion mediated by BamA.
  • The study advances our understanding of protein transport across the bacterial outer membrane.