Self-assembling proteins cages are a popular platform for encapsulating, protecting, and delivering a variety of cargo due to their tunability, increased biocompatibility, lower immunogenicity, and added functionality over other synthetic delivery agents. The natural roles of protein cages tend to be for storage and protection, but they can be repurposed for uses as nanoreactors, drug delivery vehicles, and building blocks for supramolecular structures. One of the smallest naturally occurring protein cages is the iron oxidation and storage protein, ferritin. Maxi-ferritins studied here form hollow 24mer assemblies with an outer diameter of 12 nm and an inner diameter of 8 nm at neutral pH and disassemble into dimers at very low or very high pH. Loading non-native cargo into ferritin typically involves a harsh disassembly-assembly process or requires covalent attachment of the cargo inside the cage. One ferritin that can circumvent this challenge is thermophilic ferritin from Archaeoglobus fulgidus (AfFtn), which has unique high ionic strength-dependent assembly at physiologic pH. Previous work from our lab and others has shown that specific nanoparticles or the superpositively charged green fluorescent protein, GFP(+36), can direct assembly of the ferritin cage. As described in this work, we computationally designed the first active superpositively charged enzyme, human carbonic anhydrase II, with a theoretical net overall surface charge of +21. This superpositively charged enzyme is able to induce AfFtn 24mer assembly without the need for a GFP(+36) fusion partner or additional reagents. We also investigated the charge magnitude and distribution requirements for protein cargo to initiate formation of the AfFtn cage while also examining the role of pH on cargo-templated assembly. The technologies we developed pave the way for even more generalizable AfFtn loading for the ever-expanding applications of protein nanocapsules.