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

TitleCryo-EM structures reveal multiple stages of bacterial outer membrane protein folding.
Publication TypeJournal Article
Year of Publication2022
AuthorsDoyle, MThomas, Jimah, JR, Dowdy, T, Ohlemacher, SI, Larion, M, Hinshaw, JE, Bernstein, HD
JournalCell
Volume185
Issue7
Pagination1143-1156.e13
Date Published2022 03 31
ISSN1097-4172
KeywordsBacterial Outer Membrane Proteins, Cryoelectron Microscopy, Escherichia coli, Escherichia coli Proteins, Protein Folding
Abstract

<p>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.</p>

DOI10.1016/j.cell.2022.02.016
Alternate JournalCell
PubMed ID35294859
PubMed Central IDPMC8985213
Grant ListK99 GM140220 / GM / NIGMS NIH HHS / United States
R00 GM140220 / GM / NIGMS NIH HHS / United States
ZIA DK052037 / ImNIH / Intramural NIH HHS / United States