Poster abstracts
Poster number 3 submitted by Blake Bertani
Driving lipopolysaccharide out of its membrane via an unusual ABC transporter
Blake R. Bertani (Department of Microbiology, Ohio State University), Natividad Ruiz (Department of Microbiology, Ohio State University)
Abstract:
With antibiotic resistance on the rise, the need for new antimicrobials is growing. Gram-negative organisms are particularly problematic due to their intrinsic resistance to many antibiotics. This resistance is mediated, in part, by a potent permeability barrier generated by lipolysaccharide (LPS) at the surface of the cell. This feature makes LPS biogenesis an attractive target for antimicrobial development, as inhibiting this process could sensitise Gram-negative organisms to existing anitbiotics. Additionally, LPS is essential in many organisms, and thus sufficient inhibition of LPS biogenesis could also kill directly. The synthesis of LPS is well characterized. However, how this molecule, once synthesized, traverses the cell envelope to assemble at the cell surface is not entirely understood. The process is mediated by a seven-protein complex, termed the Lpt complex (Lipopolysaccharide transport), which forms a proteinacous bridge spanning all compartments of the cell. This complex is powered by an unusual ATP-binding cassette (ABC) transporter, LptB2FG. LptB is the ATPase of the system, but the functions of the transmembrane subunits LptF/G are not well characterized. We now report evidence suggesting that LptG interacts directly with LPS during transport. Specifically, we have identified a positively charged region in LptG critical for function. Amino acid substitutions in this region confer defects in LPS biogenesis, particularly when adding more negative charge to this region of LptG. Moreover, these defects can be suppressed by activation of the BasSR system, a two-component system which controls chemical modification of LPS. This suppression by activation of BasSR requires the enzymes EptA and ArnT, which modify negatively-charged phosphates on LPS with positively charged moieties. These results suggest a direct, charge based interaction between this newly identified region of LptG and LPS. We propose LptFG directly extract LPS from the inner membrane.
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Keywords: Escherichia coli, Lipopolysaccharide Transport, Envelope Biogenesis