A virus-based nanoblock with tunable electrostatic properties.

Five different "HIS tag" mutants of cowpea mosaic virus were made by genetically introducing six contiguous histidine residues at various locations on the virus capsid. The mutant particles showed differential affinity for binding nickel, and their electrostatic properties could be controlled as a function of the protonation state of the exposed histidine sequence. The specific addressability of the HIS tag was corroborated by the selective modification of the histidine sequence with nanogold cross-linked to the Ni-NTA moiety.