Metal-templated assembly of protein cages

The ability to chemically control protein-protein interactions would allow the interrogation of dynamic cellular processes, and lead to better understanding and exploitation of self-assembled protein architectures. Yet, the direct incorporation of a simple chemical switch into highly evolved, finely tuned and extensive protein-protein interfaces is a tremendous design challenge. Here we introduce a new engineering strategy-reverse metal- templated interface redesign (rMeTIR)-which transforms a natural protein-protein interface into one that only engages in selective response to a metal ion. We have applied rMeTIR to render the self-assembly of the cage- like protein human H-ferritin controllable specifically by CuII binding, which has allowed for the first time: a) the study of the structure and stability of the isolated ferritin monomer, b) the demonstration of the primary role of peripheral H-bonding interactions in providing geometric specificity for cage assembly, and c) the modification of the interior of the ferritin cage under physiological conditions via an active encapsulation mechanism. Significantly, CuII acts as a structural template for ferritin assembly in a manner that is highly reminiscent of nucleotide sequences that template virus capsid formation, and we are employing its capacity to facilitate monomer-to-cage formation for the purposes of exploring the ferritin assembly mechanism and furthering materials applications of the ferritin nanocag