A multi-spectroscopic approach to investigate the interactions between Gramicidin A and silver nanoparticles

Heat-induced self-assembling of BSA at the isoelectric point

Materials based on ordered protein aggregates have recently received a lot of attention for their application as drug carriers, due to their biocompatibility and their ability to sequester many biological fluids. Bovine serum albumin (BSA) is a good candidate for this use due to its high availability and tendency to aggregate and gel under acidic conditions. In the present work, we employ spectroscopic techniques to investigate the heat-induced BSA aggregation at the molecular scale, in the 12-84 °C temperature range, at pH = 5 where two different isoforms of the protein are stable. Samples at low and high protein concentration are examined. With the advantage of the combined use of FTIR and CD, we recognize the aggregation-prone species and the different distribution of secondary structures, conformational rearrangements and types of aggregates, of millimolar compared to micromolar BSA solutions. Further, as a new tool, we use the Maximum Entropy Method to fit the kinetic curves to investigate the distribution of kinetic constants of the complex hierarchical aggregation process. Finally, we characterize the activation energy of the initial self-assembling step to observe that the formation of both small and large aggregates is driven by the same interactions.

Anionic nanoparticle-induced perturbation to phospholipid membranes affects ion channel function

Understanding the mechanisms of nanoparticle interaction with cell membranes is essential for designing materials for applications such as bioimaging and drug delivery, as well as for assessing engineered nanomaterial safety. Much attention has focused on nanoparticles that bind strongly to biological membranes or induce membrane damage, leading to adverse impacts on cells. More subtle effects on membrane function mediated via changes in biophysical properties of the phospholipid bilayer have received little study. Here, we combine electrophysiology measurements, infrared spectroscopy, and molecular dynamics simulations to obtain insight into a mode of nanoparticle-mediated modulation of membrane protein function that was previously only hinted at in prior work. Electrophysiology measurements on gramicidin A (gA) ion channels embedded in planar suspended lipid bilayers demonstrate that anionic gold nanoparticles (AuNPs) reduce channel activity and extend channel lifetimes without disrupting membrane integrity, in a manner consistent with changes in membrane mechanical properties. Vibrational spectroscopy indicates that AuNP interaction with the bilayer does not perturb the conformation of membrane-embedded gA. Molecular dynamics simulations reinforce the experimental findings, showing that anionic AuNPs do not directly interact with embedded gA channels but perturb the local properties of lipid bilayers. Our results are most consistent with a mechanism in which anionic AuNPs disrupt ion channel function in an indirect manner by altering the mechanical properties of the surrounding bilayer. Alteration of membrane mechanical properties represents a potentially important mechanism by which nanoparticles induce biological effects, as the function of many embedded membrane proteins depends on phospholipid bilayer biophysical properties.