Development of protein cages for encapsulation of active enzyme cargoes and their subsequent arrangement into a controllable three-dimensional array is highly desirable. However, cargo capture is typically challenging because of difficulties in achieving reversible assembly/disassembly of protein cages in mild conditions. Herein we show that by using an unusual ferritin cage protein that undergoes triggerable assembly under mild conditions, we can achieve reversible filling with protein cargoes including an active enzyme. We demonstrate that these filled cages can be arrayed in three-dimensional crystal lattices and have an additional chaperone-like effect, increasing both thermostability and enzymatic activity... More