Roles of the EnvZ/OmpR Two-Component System and Porins in Iron Acquisition in Escherichia coli

The work presented here solved a long-standing paradox of the negative effects of certain missense alleles of envZ , which codes for kinase of the EnvZ/OmpR two-component system, on the expression of ferric uptake genes. The data revealed that the constitutive envZ alleles activate the Feo- and OmpC-mediated ferrous uptake pathway to flood the cytoplasm with accessible ferrous iron. This activates the ferric uptake regulator, Fur, which inhibits ferric uptake system but cannot inhibit the feo operon due to the positive effect of activated EnvZ/OmpR. The data also revealed the importance of porins in iron homeostasis.