Coating carbon nanotubes with peptides can produce structurally specific, tunable macromolecular assemblies, University of Pennsylvania researchers report (Science, DOI: 10.1126/science.1198841). Led by biochemistry professor William F. DeGrado, the group used computational design methods to develop glycine- and alanine-rich helical peptides that wrap into a supercoiled layer around single-walled carbon nanotubes. Glycine or alanine groups are needed on one side of a peptide helix to interface with the nanotube, while residues at helical interfaces direct assembly. Other amino acids in the peptides can be altered to modulate the solubility or stability of the constructs, or functionalize the surface. In one case, DeGrado and colleagues nucleated gold nanoclu sters on the surface of a peptide-coated nanotube, creating an additional ordered layer of nanoparticles on top of the peptide layer. The peptides can also be tuned to bind to specific nanotube geometries. The overall approach provides a way to create defined and controllable structures on an otherwise featureless surface, the authors say.