Abstract
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.
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