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Purification and Characterization of the Rhizobium leguminosarum lipid A Oxidase, LpxQ
Author(s) -
Ingram Brian O'Neal,
Raetz Christian R. H.
Publication year - 2009
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.23.1_supplement.502.10
Subject(s) - chemistry , rhizobium leguminosarum , lipid a , biochemistry , hydrogen peroxide , lipid oxidation , divalent , enzyme , glucosamine , substrate (aquarium) , bacteria , rhizobiaceae , organic chemistry , biology , ecology , antioxidant , genetics , symbiosis
The lipid A component of lipopolysaccharides from the plant endosymbionts Rhizobium leguminosarum contains an unusual proximal sugar unit consisting of a 2‐amino‐2‐deoxy‐gluconate moiety in place of glucosamine. This modification results from the actions of the enzyme LpxQ, which generates the 2‐amino‐2‐deoxy‐gluconate unit from a glucosamine‐containing precursor. LpxQ is localized to the outer membrane and is dependent on molecular oxygen for activity. LpxQ was shown to be active when expressed heterologously in E. coli. Lipid A was isolated from E. coli expressing LpxE and LpxQ and was shown to be oxidized by ESI‐mass spectrometry. A new substrate and assay were developed to monitor lipid A oxidation in vitro . A purification scheme was developed. Purified LpxQ was shown to be dependent on a divalent cation and not stimulated by FAD or PQQ. Hydrogen peroxide was found to be a by‐product of lipid A oxidation. The mechanism and cofactors involved in the oxidation reaction are under investigation. This work is supported by NIH Grant R37‐GM‐51796 to C. R. H. R.