Probing bulky ligand entry in engineered archaeal ferritins

Background: A set of engineered ferritin mutants from Archaeoglobus fulgidus (Af-Ft) and Pyrococcus furiosus (Pf-Ft) bearing cysteine thiols in selected topological positions inside or outside the ferritin shell have been obtained. The two apo-proteins were taken as model systems for ferritin internal cavity accessibility in that Af-Ft is characterized by the presence of a 45 A wide aperture on the protein surface whereas Pf-Ft displays canonical (threefold) channels.