Engineered nanomaterials can alter the structure and/or function of biological membranes and membrane proteins but the underlying mechanisms remain unclear. We addressed this using a Langmuir phospholipid monolayer containing an active transmembrane protein, glucose-6-phosphatase (G6Pase). Gold nanoparticles (nAu) with varying ligand shell composition and hydrophobicity were synthesized, and their partitioning in the membrane and effects on protein activity characterized. nAu incorporation did not alter the macroscopic properties of the membrane. Atomic force microscopy showed that when co-spread with other components prior to membrane compression, nAu preferentially interacted with G6Pase and each other in a functional group-dependent manner. Under these conditions, all nAu formulations reduced G6Pase aggregation in the membrane, enhancing catalytic activity 5–6 fold. When injected into the subphase beneath pre-compressed monolayers, nAu did not affect G6Pase activity over 60 minutes, implying they were unable to interact with the protein under these conditions. A small but significant quenching of tryptophan fluorescence showed that nAu interacted with G6Pase in aqueous suspension. nAu also significantly reduced the hydrodynamic diameter of G6Pase in aqueous suspension and promoted catalytic activity, likely via a similar mechanism to that observed in co-spread monolayers. Overall, our results show that nAu can incorporate into membranes and associate preferentially with membrane proteins under certain conditions and that partitioning is dependent upon ligand shell chemistry and composition. Once incorporated, nAu can alter the distribution of membrane proteins and indirectly affect their function by improving active site accessibility, or potentially by changing their native structure and distribution in the membrane.

The safe and effective use of nanoparticles for biological applications requires a many-pronged classification of nanoparticle properties (material, coating, size, and shape) as well as biological environments. A Langmuir-film-based synthetic membrane system containing an active transmembrane protein, glucose-6-phosphatase (G6Pase), was employed to investigate the effects nanoparticle exposure as a function of membrane surface pressure. The activity of G6Pase after exposure to 5 nm gold nanoparticles functionalized with anionic, cationic, and neutral ligand coatings was found to increase by as much as 300% for both anionic and neutral particles at surface pressures less than 30 mN/m, indicating significant nanoparticle−protein interactions. Atomic force microscopy imaging was used to track the distribution of nanoparticles and G6Pase within the membranes and correlate changes in activity to the distribution of G6Pase in the membrane. Conditions which enabled the redistribution of protein in the form of solubilization or aggregation within the membrane were identified for each class of nanoparticles. This investigation demonstrates the importance of the phospholipid environment surrounding membrane proteins during exposure to nanoparticles which can impact the nanoparticle fate in terms of uptake as well as potential effects on membrane protein activity.