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Related Concept Videos

Porin Insertion in the Outer Mitochondrial Membrane01:12

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Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel...
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Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking
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Structural basis of outer membrane protein insertion by the BAM complex.

Yinghong Gu1, Huanyu Li1, Haohao Dong1

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The bacterial outer membrane protein assembly machinery (BAM) mechanism is now clearer. Structural studies reveal how BamA and associated proteins rotate to insert new outer membrane proteins (OMPs) into the cell envelope.

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Area of Science:

  • Structural Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Outer membrane proteins (OMPs) are crucial for Gram-negative bacteria, mitochondria, and chloroplasts.
  • The β-barrel assembly machinery (BAM) complex facilitates OMP insertion and folding into the outer membrane.
  • The precise mechanism of BAM-mediated OMP biogenesis remains largely unknown due to a lack of structural data.

Purpose of the Study:

  • To elucidate the mechanism of outer membrane protein insertion by the BAM complex.
  • To provide high-resolution structural insights into the Escherichia coli BAM complex.
  • To understand the dynamic interactions between BAM subunits during OMP biogenesis.

Main Methods:

  • X-ray crystallography to determine the structure of the BAM complex in different states.
  • Biochemical assays to study the function of BAM complex components.
  • Molecular dynamics simulations to analyze the dynamic movements within the BAM complex.

Main Results:

  • Two distinct crystal structures of the Escherichia coli BAM complex were determined: an inward-open state and a lateral-open state.
  • The structures reveal a ring architecture formed by the five polypeptide transport-associated domains of BamA, associated with four lipoproteins (BamB-BamE).
  • Structural and functional data indicate that rotation of the associated lipoproteins relative to BamA's β-barrel drives the insertion of nascent OMPs.

Conclusions:

  • The study provides unprecedented structural snapshots of the BAM complex, revealing its dynamic nature.
  • The findings elucidate a rotation-based mechanism for OMP insertion mediated by the BAM complex.
  • This work significantly advances our understanding of a fundamental process in the biogenesis of essential membrane proteins.