Cryo-EM structures reveal multiple stages of bacterial outer membrane protein folding

Matthew Thomas Doyle, John R. Jimah, Tyrone Dowdy, Shannon I. Ohlemacher, Mioara Larion, Jenny E. Hinshaw, Harris D. Bernstein

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Transmembrane β barrel proteins are folded into the outer membrane (OM) of Gram-negative bacteria by the β barrel assembly machinery (BAM) via a poorly understood process that occurs without known external energy sources. Here, we used single-particle cryo-EM to visualize the folding dynamics of a model β barrel protein (EspP) by BAM. We found that BAM binds the highly conserved “β signal” motif of EspP to correctly orient β strands in the OM during folding. We also found that the folding of EspP proceeds via “hybrid-barrel” intermediates in which membrane integrated β sheets are attached to the essential BAM subunit, BamA. The structures show an unprecedented deflection of the membrane surrounding the EspP intermediates and suggest that β sheets progressively fold toward BamA to form a β barrel. Along with in vivo experiments that tracked β barrel folding while the OM tension was modified, our results support a model in which BAM harnesses OM elasticity to accelerate β barrel folding.

Original languageEnglish (US)
Pages (from-to)1143-1156.e13
Issue number7
StatePublished - Mar 31 2022
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Biochemistry, Genetics and Molecular Biology


  • BAM
  • membrane dynamics
  • membrane protein folding
  • outer membrane protein
  • β barrel


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