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Topography of Lipid A Assembly and Modification in the Inner Membrane of Francisella
Author(s) -
Zhao Jinshi,
Raetz Christian R. H.
Publication year - 2011
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.25.1_supplement.940.5
Subject(s) - lipid a , bacterial outer membrane , francisella , lipopolysaccharide , francisella tularensis , biochemistry , inner membrane , lipid bilayer , chemistry , residue (chemistry) , membrane fluidity , membrane , mutant , mannose , biology , escherichia coli , gene , virulence , endocrinology
Francisella tularensis is Gram‐negative bacteria that cause tularemia in mammals. The outer leaflet of its outer membrane is formed by lipid A, the hydrophobic membrane anchor of lipopolysaccharide (LPS). However, about two thirds of the lipid A molecules in Francisella do not have a core oligosaccharide. We have discovered that LPS and free lipid A are not fully separated from each other during purification. We took advantage of a mutation in a mannosyl transferase (LpcC), which adds the proximal mannose residue to Kdo 2 ‐lipid A in the first step of outer core assembly. The LpcC mutant produces a truncated LPS with Kdo residues as the only remaining core sugars. The Kdo modified lipid A molecules lack of both the 1 and 4′‐phosphate groups, whereas free lipid A only lacks the 4′‐phosphate residue. This difference is attributed to the selectivity of the 1‐phosphatase LpxE, which located on the outer surface of the inner membrane and is dependent upon the presence of the Kdo disaccharide for activity. Likewise, LpcC, which faces the cytoplasm, is selective in vivo and in vitro for acceptor substrates with two Kdo units instead of one. Our findings have implications for the order and topography of lipid A modification reactions in the Francisella inner membrane. Supported by NIH grant GM‐51796 to C.R.H.R.