The outer membrane (OM) of Gram-negative bacteria such as
Most Gram‐negative bacteria assemble lipopolysaccharides (LPS) on their surface to form a permeability barrier against many antimicrobials. LPS is synthesized at the inner membrane and then transported to the outer leaflet of the outer membrane. Although the overall LPS structure is conserved, LPS molecules can differ in composition at the species and strain level. Some bacteria also regulate when to modify phosphates on LPS at the inner membrane in order to become resistant to cationic antimicrobial peptides. The multi‐protein Lpt trans‐envelope machine, which transports LPS from the inner to the outer membrane, must therefore handle a variety of substrates. The most poorly understood step in LPS transport is how the ATP‐binding cassette LptB2FG transporter extracts LPS from the inner membrane. Here, we define residue K34 in LptG as a site within the structural cavity of the
- NSF-PAR ID:
- 10073361
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Molecular Microbiology
- Volume:
- 109
- Issue:
- 4
- ISSN:
- 0950-382X
- Page Range / eLocation ID:
- p. 541-554
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Escherichia coli is an asymmetric bilayer with the glycolipid lipopolysaccharide (LPS) in the outer leaflet and glycerophospholipids in the inner. Nearly all integral OM proteins (OMPs) have a characteristic β-barrel fold and are assembled in the OM by the BAM complex, which contains one essential β-barrel protein (BamA), one essential lipoprotein (BamD), and three non-essential lipoproteins (BamBCE). A gain-of-function mutation inbamA enables survival in the absence of BamD, showing that the essential function of this protein is regulatory. Here, we demonstrate that the global reduction in OMPs caused by BamD loss weakens the OM, altering cell shape and causing OM rupture in spent medium. To fill the void created by OMP loss, phospholipids (PLs) flip into the outer leaflet. Under these conditions, mechanisms that remove PLs from the outer leaflet create tension between the OM leaflets, which contributes to membrane rupture. Rupture is prevented by suppressor mutations that release the tension by halting PL removal from the outer leaflet. However, these suppressors do not restore OM stiffness or normal cell shape, revealing a possible connection between OM stiffness and cell shape. -
Abstract The outer membrane is a key virulence determinant of gram‐negative bacteria. In
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