Protein encapsulation within synthetic molecular hosts

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 incommensurably larger size 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 and, upon addition of Pd(II) ions (M) and additional ligands (L), M 12 L 24 coordination nanocages self-assembled around the protein. Because of the well-defined host framework, the protein-encapsulated structure could be analysed by NMR spectroscopy, ultracentrifugation and X-ray crystallography. Protein encapsulation in molecular cages has the potential to alter protein function and aid crystallization. Here, ubiquitin is encapsulated within a giant coordination cage; the protein is attached to a bidentate ligand, and the cage self-assembles upon addition of capping ligands and Pd(II) ions.