Reengineering of an artificial protein cage for efficient packaging of active enzymes

Protein cages that readily encapsulate active enzymes of interest present useful nanotools for delivery and catalysis, wherein those with programmable disassembly characteristics serve as particularly attractive platforms. Here we establish a general guest packaging system based on an artificial protein cage, TRAP-cage, the disassembly of which can be induced by the addition of reducing agents. In this system, TRAP-cage with SpyCatcher moieties in the lumen was prepared using genetic modification of the protein building block and assembled into a cage structure with either monovalent gold ions or molecular crosslinkers. The resulting protein cage can efficiently capture guest proteins equipped with a SpyTag by simply mixing them in aqueous solution. This post-assembly loading system which circumvents the exposure of guests to thiol-reactive crosslinkers, enables packaging of enzymes possessing a catalytic cysteine or a metal cofactor while retaining their catalytic activity.