Cargo protein of a type 1 encapsulin nanocompartment. An iron-binding protein probably involved in iron mineralization in the encapsulin nanocompartment. 2 different cargo proteins have been identified (IMEF and Fer); when both are expressed in E.coli with the shell protein only IMEF is detected within the nanocompartment. E.coli expressing all 3 genes stores the largest amount of iron and is protected from Fe/H2O2-induced oxidative stress. Binds 1 2Fe-2S cluster. The N-terminus (targeting peptide) is probably responsible for targeting to the encapsulin nanocompartment. Belongs to the 2Fe2S plant-type ferredoxin family.