Credit: © 2006 RSC

Biological molecules are increasingly used in nanotechnology, in part because of their self-assembly properties. In particular, coat proteins, which usually surround viruses, have the potential to self-assemble and encapsulate and transport drugs or DNA. However, it is not easy to control the capsule shape.

Now, Jeroen Cornelissen, of Radboud University, and co-workers1 in the Netherlands have made new highly stable nanoparticles by combining coat proteins with a polymer, polystyrene sulphonate. Although polymer–coat-protein nanoparticles have been synthesized before, the authors find instead of the naturally occurring larger capsule shape, the coat proteins surround 100% of the polymers forming new smaller (16 nm) particles that remain stable for several weeks and over a wide pH range.

Cornelissen and co-workers conclude that electrostatic interactions between the polymer and coat proteins must be important in forming smaller nanoparticles. When the relative concentration of the polymer is decreased, interactions between the coat proteins appear to dominate particle formation, resulting in the naturally occurring larger shape. As parts of the N-terminus, which is involved in binding, were found to be missing in all the coat proteins, the authors now plan to examine the role such absences play in nanoparticle formation.