Cell Reports
Volume 23, Issue 9, 29 May 2018, Pages 2782-2794
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Article
The WD40 Protein BamB Mediates Coupling of BAM Complexes into Assembly Precincts in the Bacterial Outer Membrane

https://doi.org/10.1016/j.celrep.2018.04.093Get rights and content
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Highlights

  • Several BAM complexes sit together in an assembly precinct

  • Assembly precincts are distributed right across the bacterial cell surface

  • The BamB and BamA subunits mediate BAM-BAM interactions

  • Assembly precincts potentiate porin trimerization by neigboring BAM complexes

Summary

The β-barrel assembly machinery (BAM) complex is essential for localization of surface proteins on bacterial cells, but the mechanism by which it functions is unclear. We developed a direct stochastic optical reconstruction microscopy (dSTORM) methodology to view the BAM complex in situ. Single-cell analysis showed that discrete membrane precincts housing several BAM complexes are distributed across the E. coli surface, with a nearest neighbor distance of ∼200 nm. The auxiliary lipoprotein subunit BamB was crucial for this spatial distribution, and in situ crosslinking shows that BamB makes intimate contacts with BamA and BamB in neighboring BAM complexes within the precinct. The BAM complex precincts swell when outer membrane protein synthesis is maximal, visual proof that the precincts are active in protein assembly. This nanoscale interrogation of the BAM complex in situ suggests a model whereby bacterial outer membranes contain highly organized assembly precincts to drive integral protein assembly.

Keywords

beta-barrel assembly
membrane proteins
membrane domains
membrane super-complexes
outer membrane biogenesis

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