Supramolecular Assembly and Coalescence of Ferritin Cages Driven by Designed Protein–Protein Interactions

A genetically encoded system for expression of supramolecular protein assemblies (SMPAs) based on a fusion construct between ferritin and citrine (YFP) was transferred from a mammalian to a bacterial host. The assembly process is revealed to be independent of the expression host, while dimensions and level of order of the assembled structures were influenced by the host organism. An additional level of interactions, namely, coalescence between the preformed SMPAs, was observed during the purification process. SAXS investigation revealed that upon coalescence, the local order of the individual SMPAs was preserved. Finally, the chaotropic agent urea effectively disrupted both the macroscopic coalescence and the interactions at the nanoscale until the level of the single ferritin cage.