A synthetic mimic of viral structure has been constructed by the synergistic co-assembly of a 16-amino acid peptide and plasmid DNA. The rational design of this short peptide, including segments for binding DNA and forming beta-sheet, is inspired by viral capsid protein. The resulting nanostructures, which we term nanococoons, appear as ellipsoids of virus-like dimension (65 x 47 nm) and display repeating stripes of similar to 4 nm wide. We propose that the co-assembly process involves DNA as a template to assist the organization of peptide strands by electrostatic interaction, while the bilayer beta-sheets and their lateral association stabilize the peptide capsid and organize the DNA within. The hierarchy affords an extremely stable structure, protecting peptide and DNA against enzymatic digestion. It opens a new and facile avenue to fabricate viral alternatives with diverse functions.