Overexpression of the waaZ Gene Leads to Modification of the Structure of the Inner Core Region of Escherichia coli Lipopolysaccharide, Truncation of the Outer Core, and Reduction of the Amount of O Polysaccharide on the Cell Surface

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Abstract
The waa gene cluster is responsible for the biosynthesis of the lipopolysaccharide (LPS) core region in Escherichia coli and Salmonella. Homologs of the waaZ gene product are encoded by the waa gene clusters of Salmonella enterica and E. coli strains with the K-12 and R2 core types. Overexpression of WaaZ in E. coli and S. enterica led to a modified LPS structure showing core truncations and (where relevant) to a reduction in the amount of O-polysaccharide side chains. Mass spectrometry and nuclear magnetic resonance spectroscopy were used to determine the predominant LPS structures in an E. coli isolate with an R1 core (waaZ is lacking from the type R1 waa gene cluster) with a copy of the waaZ gene added on a plasmid. Novel truncated LPS structures, lacking up to 3 hexoses from the outer core, resulted from WaaZ overexpression. The truncated molecules also contained a KdoIII residue not normally found in the R1 core.