1.S.6.1.3
The encapsulin shell protein of 280 aas with four equidistant peaks of moderate hydrophobicity. This encapsulin nanocompartment protein is formed by 60 subunits; monomers form pentamers which assemble to form shells. There are 12 pores where the pentamers meet as well as 3-fold axis channels and dimer channels; none are larger than 3-4 Angstroms in diameter. The N-terminus of the protein is inside the shell, the C-terminus is outside (He et al. 2016). The shell component is for a type 1 encapsulin nanocompartment. It assembles into proteinaceous icosahedral shells 24 nm in diameter in the presence and absence of its ferritin cargo protein. The center of cargo-loaded nanocompartments is loaded with iron. The empty encapsulin nanocompartment sequesters about 2200 Fe ions while the cargo-loaded nanocompartment can maximally sequester about 4150 Fe ions. It does not have detectable ferroxidase activity (He et al. 2016).