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Publication Abstract from PubMed

Transmembrane beta barrel proteins are folded into the outer membrane (OM) of Gram-negative bacteria by the beta 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 beta barrel protein (EspP) by BAM. We found that BAM binds the highly conserved "beta signal" motif of EspP to correctly orient beta strands in the OM during folding. We also found that the folding of EspP proceeds via "hybrid-barrel" intermediates in which membrane integrated beta 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 beta sheets progressively fold toward BamA to form a beta barrel. Along with in vivo experiments that tracked beta barrel folding while the OM tension was modified, our results support a model in which BAM harnesses OM elasticity to accelerate beta barrel folding.

Cryo-EM structures reveal multiple stages of bacterial outer membrane protein folding.,Doyle MT, Jimah JR, Dowdy T, Ohlemacher SI, Larion M, Hinshaw JE, Bernstein HD Cell. 2022 Mar 31;185(7):1143-1156.e13. doi: 10.1016/j.cell.2022.02.016. Epub , 2022 Mar 15. PMID:35294859^[4]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.