Preparation of a Cross-Linked Porous Protein Crystal Containing Ru Carbonyl Complexes as a CO-Releasing Extracellular Scaffold

Protein crystals generally are stable solid protein assemblies. Certain protein crystals are suitable for use as nanovessels for immobilizing metal complexes. Here we report the preparation of ruthenium carbonyl-incorporated cross-linked hen egg white lysozyme crystals (Ru center dot CL-HEWL). Ru center dot CL-HEWL retains a Ru carbonyl moiety that can release CO, although a composite of Ru carbonyl-HEWL dissolved in buffer solution (Ru center dot HEWL) does not release CO. We found that treatment of cells with Ru center dot CL-HEWL significantly increased nuclear factor kappa B (NF-kappa B) activity as a cellular response to CO. These results demonstrate that Ru center dot CL-HEWL has potential for use as an artificial extracellular scaffold suitable for transport and release of a gas molecule.