Affiliation:
1. Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Milan, Italy
2. Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milan, Italy
3. Dipartimento di Biologia, Università degli Studi di Milano, Milan, Italy
Abstract
ABSTRACT
The outer membrane (OM) of gram-negative bacteria is an asymmetric lipid bilayer that protects the cell from toxic molecules. Lipopolysaccharide (LPS) is an essential component of the OM in most gram-negative bacteria, and its structure and biosynthesis are well known. Nevertheless, the mechanisms of transport and assembly of this molecule in the OM are poorly understood. To date, the only proteins implicated in LPS transport are MsbA, responsible for LPS flipping across the inner membrane, and the Imp/RlpB complex, involved in LPS targeting to the OM. Here, we present evidence that two
Escherichia coli
essential genes,
yhbN
and
yhbG
, now renamed
lptA
and
lptB
, respectively, participate in LPS biogenesis. We show that mutants depleted of LptA and/or LptB not only produce an anomalous LPS form, but also are defective in LPS transport to the OM and accumulate de novo-synthesized LPS in a novel membrane fraction of intermediate density between the inner membrane (IM) and the OM. In addition, we show that LptA is located in the periplasm and that expression of the
lptA-lptB
operon is controlled by the extracytoplasmic σ factor RpoE. Based on these data, we propose that LptA and LptB are implicated in the transport of LPS from the IM to the OM of
E. coli
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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