Kinetics and Structure of Self-Assembled Flagellin Monolayers on Hydrophobic Surfaces in the Presence of Hofmeister Salts: Experimental Measurement of the Protein Interfacial Tension at the Nanometer Scale

Abstract

In the present study, we monitor the adsorption−desorption kinetics and adsorbed layer structure of the bacterial protein flagellin in the presence of Hofmeister salts by a surface sensitive label-free optical biosensor (optical waveguide lightmode spectroscopy, OWLS). The recorded OWLS data were analyzed by a computer code using a set of coupled differential equations modeling the adsorption−desorption process. By supposing reversibly and irreversibly adsorbed protein states with different adsorption footprints, the kinetic data could be perfectly fitted. We revealed that the proteins adsorbing in the presence of kosmotropic salts had smaller footprints, leading to a more oriented and densely packed layer. Kosmotropic salts increased both the adsorption rate constant and the transition rate constants from the reversibly to the irreversibly adsorbed state. In contrast, chaotropic salts increased the desorption rate constant and led to decreased adsorbed mass and a more loosely packed film. Neither circular dichroism spectroscopy in bulk solutions or Fourier transform infrared spectroscopy of surface-adsorbed flagellins could reveal significant structural changes due to the presence of the Hofmeister salts, and supported our conclusions about the adsorption mechanism. On the basis of the measured kinetic and structural data (footprints of adsorbed proteins), we developed a model to calculate the protein−water-substrate interfacial tension in the presence of Hofmeister salts, and compared the experimentally obtained values with related literature data. The calculated values are consistent with previously published data of surface tension changes, andto the best of our knowledgerepresent the first experimental results for this quantity.

Glycocalyx regulates the strength and kinetics of cancer cell adhesion revealed by biophysical models based on high resolution label-free optical data

“…On the contrary, a moderately dense glycocalyx layer is suggested to promote clustering of integrins on cell surfaces 23 www.nature.com/scientificreports/ interactions of two types of glycocalyx components ("stiff beams" and "flexible chains") with each other, the deformable cell membrane and the external ligands 77 . Based on our earlier findings on the Hofmeister-phenomenon of kosmotropic salting-out [82][83][84] , we raise a complementary argumentation. Namely, dominant side chains of the glycocalyx (e.g., the sulfate and carboxyl groups of heparan or chondroitin sulfate, and hyaluronic acid, respectively) are considered highly kosmotropic agents 85 , ordering adjacent water molecules stronger than integrin side chains do (containing, amongst others, non-kosmotropic beta-sheet structures).…”

Grating-coupled interferometry reveals binding kinetics and affinities of Ni ions to genetically engineered protein layers

“…PCP-LIP refers to a thin, quasi-planar polycarboxylate polymer (PCP) coating on the waveguide where lipophilic (LIP) groups are pre-immobilized to the PCP chains. This type of sensor chip can be used for capturing ligands through hydrophobic interactions (according to our previous results, flagellins can be efficiently captured in this way 52,62,63 ). The PCH chip carries a thick polycarboxylate-based hydrogel coating with free carboxylic functions to which proteins can be covalently coupled through EDC/NHS (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/N-hydroxysuccinimide) linking chemistry.…”

Role of Protein-Water Interface in the Stacking Interactions of Granum Thylakoid Membranes—As Revealed by the Effects of Hofmeister Salts

“…Based on the formal match of the theory with that of hydrophobic effects ( Tanford, 1979 ), Hofmeister effects could be interpreted as a modification of hydrophobic/hydrophilic interactions, described by the surface terms of the Gibbs free energy. Since then, a row of experimental and theoretical evidences supporting the predictions of the theory have been published ( Khoroshyy et al, 2013 ; Szalontai et al, 2013 ; Bogár et al, 2014 ; Násztor et al, 2016 ; Násztor et al, 2017 ; Kovacs et al, 2018 ).…”