Structural and Functional Effects of Cu Metalloprotein-Driven Silver Nanoparticle Dissolution

Abstract

Interactions of a model Cu-metalloprotein, azurin, with 10-100 nm silver nanoparticles (NPs) were examined to elucidate the role of oxidative dissolution and protein interaction on the biological reactivity of NPs. Although minimal protein and NP structural changes were observed upon interaction, displacement of Cu(II) and formation of Ag(I) azurin species under aerobic conditions implicates Cu(II) azurin as a catalyst of NP oxidative dissolution. Consistent with NP oxidation potentials, largest concentrations of Ag(I) azurin species were recorded in reaction with 10 nm NPs (>50%). Apo-protein was also observed under anaerobic reaction with NPs of all sizes and upon aerobic reaction with larger NPs (>20 nm), where NP oxidation is slowed. Cu(II) azurin displacement upon reaction with NPs was significantly greater than when reacted with Ag(I)(aq) alone. Regardless of NP size, dialysis experiments show minimal reactivity between azurin and the Ag(I)(aq) species formed as a result of NP oxidative dissolution, indicating Cu displacement from azurin occurs at the NP surface. Mechanisms of azurin-silver NP interaction are proposed. Results demonstrate that NP interactions not only impact protein structure and function, but also NP reactivity, with implications for targeting, uptake, and cytotoxicity.

Transformations of silver nanoparticles in wastewater effluents: links to Ag bioavailability

“…Once the NP or related transformed species interact with a physiologically active site on the cell surface, they may affect the cell metabolism and disrupt the cellular homeostasis [35]. If the interaction is strong enough to overwhelm the stress responses, which arise due to a disruption in homeostasis, a toxic outcome will ensue [36]. The bioavailability of a NP can be inferred by characterizing a biological end-point; these biological end-points will be different for different organisms (e.g., algae, bacteria, and fish) and may include metal bioaccumulation (sorption or uptake), photosynthetic activity, motility, respiration and growth [35].…”

“…Algal cells are surrounded by cell walls, which are an important barrier to the physical penetration of ENMs into the cells [36]. Indeed, the importance of the cell wall in protecting the algal cells from Ag NP internalization has been demonstrated by Piccapietra et al [39], as they have found higher rate of Ag internalization in the cell-wall-free strain of C. reinhardtii as compared to the wild-type strain.…”

“…Nonetheless, it was also shown that cell walls are semipermeable and that they may still allow the passage of entities on the nano-scale [15]. Finally, it has been shown that the emergence of a toxic outcome does not necessarily require the internalization of NPs into the cells [36].…”

“…This bio-physical interaction may include processes that disturb the phospholipid bilayers [36]. Depending on the ENM surface characteristics, this interaction may potentially lead to gelation or "hole" formation in the phospholipid bilayer.…”

“…If the ENM interaction is so intense that the stress response is overcome, then a toxic outcome will ensue [36]. Another important consideration that should be accounted for is how the interaction of algae or algal exudates (organic substances excreted from algae) with Ag NPs would influence their speciation [50,51].…”