Protein encapsulation has long attracted many chemists and biologists because of its potential to control the structure and functions of proteins, but has been a daunting challenge because of their sensitive nature and incommensurably larger size as compared with common synthetic hosts. Here, we report the encapsulation of a small protein, ubiquitin, within giant coordination cages. The protein was attached to one bidentate ligand (L) (1) and, upon addition of
Pd(II) ions (M) and additional ligands (2), M12L24 coordination nanocages self-assembled around the protein (3). Due to the well-defined host framework, the protein-encapsulated structure could be well analyzed by NMR spectroscopy, ultracentrifugation, and X-ray crystallography.
We demonstrated that ubiquitin (roughly 4 nm in diameter) was fully encapsulated within the 6.3 nm coordination sphere.