A crystalline protein assembly of cypovirus polyhedra was engineered to develop a carbon monoxide (CO) releasing extracellular scaffold by immobilizing ruthenium carbonyls. The molecular design includes introduction of a hexahistidine tag to the C-terminus and provides immobilization of about 2-fold more Ru carbonyls per protein monomer and effectively releases three times more CO for activation of nuclear factor kappa B (NF-kappa B) in living cells relative to wild-type polyhedra with Ru carbonyls.