Interaction of viral ATPases with nucleotides measured with a microcantilever

We report label-free measurements of the interaction between nucleotides and proteins using a cantilever-based sensor functionalized with viral ATPases. In the present study, immobilization curves and AFM imaging revealed the existence of two immobilization regimes over the wide range of gp19 concentrations assayed. Proteins start forming a monolayer over the surface and subsequently reorganize in three-dimensional aggregates of piled gp19 at higher protein concentrations. We show that in this regime the response to the binding of ATP is completely distinct to the observed stepped behavior of the monolayer regime described before. ATP interaction modifies the conformation of the proteins that build the clusters and, due to the interaction with the nucleotide, the cohesion of the aggregates is affected. As both ATP and AMP-PNP (a non hydrolyzable analog) can bind the gp19 aggregates producing a genuine deflection of the microcantilever, the competitive binding between them can be also detected in real time. Our hybrid bionanomechanical device reveals exciting opportunities to adsorb chemical species for the understanding of enzymatic behavior.