Exploring the microbial metalloproteome using MIRAGE

The microbial metalloproteome has been largely unexplored. Using the metalloproteomics approach MIRAGE (Metal Isotope native RadioAutography in Gel Electrophoresis) we have been able to explore the soluble Fe and Zn metalloproteome of Escherichia coli. The protein identification by MS/MS typically resulted in several overlapping proteins for each metal containing spot. Using the E. coli genome annotation the proteins relevant to the iron and zinc proteome were selected. Superoxide dismutase (SodB) was found to be the major iron protein after cultivation with a normal iron concentration of 6 μM. Upon an elevated iron concentration of 40 μM, ferritin (FtnA) became dominant. Under both conditions 90% of the iron was associated with just three different proteins: superoxide dismutase (SodB), ferritin (FtnA) and bacterioferritin (Bfr). The uncharacterized proteins YgfK and XdhD were found to be significant iron containing proteins under elevated iron conditions. The zinc proteome of E. coli experiencing zinc stress was dominated by ZraP, a putative zinc storage protein.