Polymer Free Volume Effects on Protein Dynamics in Polystyrene Revealed by Single-Molecule Spectroscopy

Abstract

Protein–polymer interactions are critical to applications ranging from biomedical devices to chromatographic separations. The mechanistic relationship between the microstructure of polymer chains and protein interactions is challenging to quantify and not well studied. Here, single-molecule microscopy is used to compare the dynamics of two model proteins, α-lactalbumin and lysozyme, at the interface of uncharged polystyrene with varied molecular weights. The two proteins exhibit different surface interaction mechanisms despite having a similar size and structure. α-Lactalbumin exhibits interfacial adsorption–desorption with residence times that depend on polymer molecular weight. Lysozyme undergoes a continuous time random walk at the polystyrene surface with residence times that also depend on the molecular weight of polystyrene. Single-molecule observables suggest that the hindered continuous time random walk dynamics displayed by lysozyme are determined by the polystyrene free volume, a finding supported by thermal annealing and solvent quality studies. Hindered dynamics are dominated by short-range hydrophobic interactions where the contributions of electrostatic forces are negligible. This work establishes a relationship between the microscale structure (i.e., free volume) of polystyrene polymer chains to nanoscale interfacial protein dynamics.

Non-Brownian Interfacial Diffusion: Flying, Hopping, and Crawling

“…Conceptually, this is due to the fact that adsorption of a solute molecule actually involves the displacement of solvent molecules, so adsorption from liquid solution can actually be considered an activated process with an activation energy associated with the solvent bindings energy. , We characterized the intermittent diffusion of adsorbate molecules at the interface between a hydrophobic surface and methanol–water solution, where the concentration of methanol in solution was varied to tune the strength of the surface–adsorbate interaction, and therefore the sticking coefficient. Consistent with theoretical predications of bulk-mediated surface diffusion, the flight lengths and surface diffusion coefficient (Figure f) increased as the hydrophobic attraction decreased. ,, …”

Super-resolution Microscopy with Single Molecules in Biology and Beyond–Essentials, Current Trends, and Future Challenges

“…The capability to detect and localize individual emitters to investigate e.g. the distribution of catalysis activity on different areas of a nanoparticles, − or to observe the behavior of separation polymers, , avoiding ensemble averaging and revealing surprising heterogeneity, has turned out to be immensely powerful in this area. Another area involves single molecules interacting with metallic nanoantennas in order to observe nanoscale properties such as hot spots involved in surface-enhanced Raman scattering; − indeed various combinations of plasmonics with super-resolution have recently been reviewed .…”

Single-Molecule Dynamics Reflect IgG Conformational Changes Associated with Ion-Exchange Chromatography

“…Traditional two-dimensional (2D) single-molecule studies are not ideal for studying realistic interactions with stationary phases. ,,,, Point spread function engineering is one way to encode three-dimensional (3D) information in a 2D image. − The importance of knowledge of analyte motion in three dimensions was previously demonstrated by investigating the influence of the types of particle structures, flow regimes, and dynamics in the column. These examples highlight the advantages of investigating not only the kinetics ,, of protein interactions at stationary phases but also protein motion in 3D.…”

“…35−38 The importance of knowledge of analyte motion in three dimensions was previously demonstrated by investigating the influence of the types of particle structures, 39 flow regimes, and dynamics 40 in the column. These examples highlight the advantages of investigating not only the kinetics 33,41,42 of protein interactions at stationary phases but also protein motion in 3D.…”