Cohen-Khait, R. | bioRxiv Science

bioRxiv2022

Peptidoglycan maturation controls spatiotemporal organisation of outer membrane proteins in Escherichia coli

Linkages between the outer membrane of Gram-negative bacteria and the peptidoglycan layer are crucial to the maintenance of cellular integrity and enable survival in challenging environments1-5. The functionality of the outer membrane relies on outer membrane proteins (OMPs), which are inserted by the {beta}-barrel assembly machine, BAM6, 7. Previous work has shown that growing Escherichia coli cells segregate old OMPs towards the poles by an unknown mechanism8. Here, we demonstrate that peptidoglycan underpins the spatiotemporal organisation of OMPs. Mature, tetrapeptide-rich peptidoglycan binds to BAM components and suppresses OMP foldase activity. Nascent peptidoglycan, which is enriched in pentapeptides and concentrated at septa9, associates with BAM poorly and has little impact on its activity, leading to preferential insertion of OMPs at division sites. Synchronising OMP biogenesis to cell wall growth enables bacteria to replenish their OMPs by binary partitioning. Our study reveals that Gram-negative bacteria coordinate the assembly of two major cell envelope layers by rendering OMP biogenesis responsive to peptidoglycan maturation. This coordination offers new possibilities for the design of antibiotics that disrupt cell envelope integrity.

microbiology↗

bioRxiv2021

Colicin-mediated transport of DNA through the iron transporter FepA

Colicins are protein antibiotics used by bacteria to eliminate competing Escherichia coli. Colicins frequently exploit outer membrane (OM) nutrient transporters to penetrate through the strictly impermeable bacterial cellular envelope. Here, applying live-cell fluorescence imaging we were able to follow colicin B (ColB) into E. coli and localize it within the periplasm. We further demonstrate that single-stranded DNA coupled to ColB is also transported into the periplasm, emphasizing that the import routes of colicins can be exploited to carry large cargo molecules into bacteria. Moreover, we characterize the molecular mechanism of ColB association with its OM receptor FepA, applying a combination of photo-activated crosslinking, mass spectrometry, and structural modeling. We demonstrate that complex formation is coincident with a large-scale conformational change in the colicin. Finally In vivo crosslinking experiments and supplementary simulations of the translocation process indicate that part of the colicin engages active transport by disguising itself to part of the cellular receptor.

microbiology↗