Poster abstracts

Poster number 30 submitted by Blake Bertani

Genetic evidence for interaction of LptG with lipolysaccharide during transport in Escherichia coli

Blake R. Bertani (Department of Microbiology)

Abstract:
Gram-negative pathogens are often of special clinical significance, due to their innate resistance to a number of existing antibiotics. This resistance is conferred, in part, by the nature of their cell envelope; more specifically, the presence of an outer membrane containing lipopolysaccharide (LPS) in its outer leaflet. This outer membrane generates an effective permeability barrier that protects Gram-negative organisms from a variety of harmful compounds, including hydrophobic antibiotics. In light of this, LPS biogenesis becomes an attractive target for inhibition when attempting to deal with Gram-negative infections, as in so doing one may be able to sensitize these organisms to existing antimicrobials, or potentially eliminate them directly, as in many Gram negatives, LPS is essential. This work focuses on the transport of LPS from the site of synthesis, at the inner membrane, to its final location, the outer leaflet of the outer membrane. This transport is mediated by a seven member protein complex, termed the Lpt complex (for lipopolysaccharide transport), which spans from the cytoplasm to the outer membrane as a proteinaceous bridge. LPS extraction from the inner membrane and its transport to the outer membrane is powered by the LptB2FG ABC transporter. While it is known that LptB functions as an ATPase, the function of the membrane components LptF and LptG in LPS transport is not well understood. Here, we report genetic evidence suggesting that LptG may interact with LPS during transport. Specifically, we have identified a group of periplasmic residues in LptG that are important for Lpt function. Notably, defects conferred by substitutions in this domain can be suppressed by mutations that activate the two-component system BasSR, which is involved in regulating chemical modifications in LPS. Together, our results suggest that LptFG may directly extract LPS from the inner membrane.

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Keywords: Lipopolysaccharide Transport , Envelope Biogenesis, Escherichia coli