A Novel Biometallic Interface: High Affinity Tip-AssociatedBinding by Pilin-Derived Protein Nanotubes

The type IV pili of Pseudomonas aeruginosa are essentially protein nanofibres composed of multiple copies of a single pilin subunit. Type IV pili extend from the bacterial surface, and mediate specific adherence to biotic and abiotic surfaces. While deletion of the N-terminal region of the pilin's *-helix allows for the ready expression of a highly soluble monomeric pilin protein, incubation of the monomeric protein with undecanethiol results in pilin oligomerization into protein nanotubes. In the present study, the ability of pilin-derived protein nanotubes to bind to grade 304 stainless steel surfaces was evaluated. Protein nanotubes bound to stainless steel with high affinity. Protein nanotube surface binding was observed to be a tip-associated event through competitive inhibition with a synthetic peptide corresponding to the pilin's C-terminal receptor binding domain. AFM studies established that the protein nanotubes utilize the pilin receptor binding domain to directly interact with the steel surface, demonstrating a 2-fold higher adhesive force for grain boundaries than for regions within grains. The adhesive force of the pilin receptor binding domain with the steel surface was determined by two methods and was conservatively estimated to be in the order of 26–55 pN/molecular interaction. Direct, specific binding of protein nanotubes, and/or receptor binding domain composite materials to a steel surface generates a novel metallo-biomolecular interface that forms preferentially on grain boundaries, enhancing the potential for these unique nanostructures in the development of biologically amenable nanosystems.