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A cluster of residues in the lipopolysaccharide exporter that selects substrate variants for transport to the outer membrane
Author(s) -
Bertani Blake R.,
Taylor Rebecca J.,
Nagy Emma,
Kahne Daniel,
Ruiz Natividad
Publication year - 2018
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.14059
Subject(s) - bacterial outer membrane , inner membrane , lipopolysaccharide , biology , cell envelope , membrane , escherichia coli , residue (chemistry) , bacteria , biochemistry , transporter , membrane transport protein , biophysics , transport protein , microbiology and biotechnology , membrane protein , gene , genetics , endocrinology
Summary 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 LptB 2 FG transporter extracts LPS from the inner membrane. Here, we define residue K34 in LptG as a site within the structural cavity of the Escherichia coli LptB 2 FG transporter that interacts electrostatically with phosphates on unmodified LPS. Alterations to this residue cause transport defects that are suppressed by the activation of the BasSR two‐component signaling system, which results in modifications to the LPS phosphates. We also show this residue is part of a larger site in LptG that differentially contributes to the transport of unmodified and modified LPS.