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Identification of Two Inner-Membrane Proteins Required for the Transport of Lipopolysaccharide to the Outer Membrane of Escherichia coli

Natividad Ruiz, Luisa S. Gronenberg, Daniel Kahne and Thomas J. Silhavy
Proceedings of the National Academy of Sciences of the United States of America
Vol. 105, No. 14 (Apr. 8, 2008), pp. 5537-5542
Stable URL: http://www.jstor.org/stable/25461639
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Identification of Two Inner-Membrane Proteins Required for the Transport of Lipopolysaccharide to the Outer Membrane of Escherichia coli
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Abstract

The outer membrane (OM) of most Gram-negative bacteria contains lipopolysaccharide (LPS) in the outer leaflet. LPS, or endotoxin, is a molecule of important biological activities. In the host, LPS elicits a potent immune response, while in the bacterium, it plays a crucial role by establishing a barrier to limit entry of hydrophobic molecules. Before LPS is assembled at the OM, it must be synthesized at the inner membrane (IM) and transported across the aqueous periplasmic compartment. Much is known about the biosynthesis of LPS but, until recently, little was known about its transport and assembly. We applied a reductionist bioinformatic approach that takes advantage of the small size of the proteome of the Gram-negative endosymbiont Blochmannia floridanus to search for novel factors involved in OM biogenesis. This led to the discovery of two essential Escherichia coli IM proteins of unknown function, YjgP and YjgQ, which are required for the transport of LPS to the cell surface. We propose that these two proteins, which we have renamed LptF and LptG, respectively, are the missing transmembrane components of the ABC transporter that, together with LptB, functions to extract LPS from the IM en route to the OM.

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