Fur Activates Expression of the 2-Oxoglutarate Oxidoreductase Genes (oorDABC) in Helicobacter pylori

Helicobacter pylori is a highly successful pathogen that colonizes the gastric mucosa of similar to 50% of the world's population. Within this colonization niche, the bacteria encounter large fluctuations in nutrient availability. As such, it is critical that this organism regulate expression of key metabolic enzymes so that they are present when environmental conditions are optimal for growth. One such enzyme is the 2-oxoglutarate (alpha-ketoglutarate) oxidoreductase (OOR), which catalyzes the conversion of alpha-ketoglutarate to succinyl coenzyme A (succinyl-CoA) and CO2. Previous studies from our group suggested that the genes that encode the OOR are activated by iron-bound Fur (Fe-Fur); microarray analysis showed that expression of oorD, oorA, and oorC was altered in a fur mutant strain of H. pylori. The goal of the present work was to more thoroughly characterize expression of the oorDABC genes in H. pylori as well as to define the role of Fe-Fur in this process. Here we show that these four genes are cotranscribed as an operon and that expression of the operon is decreased in a fur mutant strain. Transcriptional start site mapping and promoter analysis revealed the presence of a canonical extended -10 element but a poorly conserved -35 element upstream of the +1. Additionally, we identified a conserved Fur binding sequence similar to 130 bp upstream of the transcriptional start site. Transcriptional analysis using promoter fusions revealed that this binding sequence was required for Fe-Fur-mediated activation. Finally, fluorescence anisotropy assays indicate that Fe-Fur specifically bound this Fur box with a relatively high affinity (dissociation constant [K-d] = 200 nM). These findings provide novel insight into the genetic regulation of a key metabolic enzyme and add to our understanding of the diverse roles Fur plays in gene regulation in H. pylori.