Downregulation of Tsx and OmpW and upregulation of OmpX are required for iron homeostasis in Escherichia coli.

Upregulation of outer membrane (OM) proteins was systematically investigated in response to poor iron availability in the host and natural environments, but downregulation of OM proteins was ill-defined in this response. We utilized proteomic methodologies to characterize altered OM proteins in the sarcosine-insoluble fraction of Escherichia coli K12 cultured in LB medium with iron limitation. Notably, three novel proteins, Tsx, OmpW, and OmpX, related to iron homeostasis were identified; Tsx and OmpW were downregulated, and OmpX was upregulated. These alterations were functionally validated with the use of gene overexpression and deletion methods. Of the two downregulated proteins, Tsx was more sensitive to an iron-deficient environment than OmpW. In addition, the significantly negative correlation between Tsx with OmpW was achieved when overexpressed strains were used. These findings strongly indicate that the downregulation of Tsx and OmpW and the upregulation of OmpX are required for iron homeostasis in E. coli.