The Role of Lys147 in the Interaction between MPSA-Gold Nanoparticles and the α‑Hemolysin Nanopore

Abstract

Single channel recordings were used to determine the effect of direct electrostatic interactions between sulfonate-coated gold nanoparticles and the constriction of the Staphylococcus aureus α-hemolysin protein channel on the ionic current amplitude. We provide evidence that Lys147 of α-hemolysin can interact with the sulfonate groups at the nanoparticle surface, and these interactions can reversibly block 100% of the residual ionic current. Lys147 is normally involved in a salt bridge with Glu111. The capture of a nanoparticle leads to a partial current block at neutral pH values, but protonation of Glu111 at pH 2.8 results in a full current block when the nanoparticle is captured. At pH 2.8, we suggest that Lys147 is free to engage in electrostatic interactions with sulfonates at the nanoparticle surface. To verify our results, we engineered a mutation in the α-hemolysin protein, where Glu111 is substituted by Ala (E111A), thus removing Glu111–Lys147 interactions and facilitating Lys147–sulfonate electrostatic interactions. This mutation leads to a 100% current block at pH 2.8 and a 92% block at pH 8.0, showing that electrostatic interactions are formed between the nanopore and the nanoparticle surface. Besides demonstrating the effect of electrostatic interactions on cross channel ionic current, this work offers a novel approach to controlling open and closed states of the α-hemolysin nanopore as a function of external gears