On the relationship between peptide adsorption resistance and surface contact angle: a combined experimental and simulation single-molecule study

The force-induced desorption of single peptide chains from mixed OH/CH3-terminated self-assembled monolayers is studied in closely matched molecular dynamics simulations and atomic force microscopy experiments with the goal to gain microscopic understanding of the transition between peptide adsorption and adsorption resistance as the surface contact angle is varied. In both simulations and experiments, the surfaces become adsorption resistant against hydrophilic as well as hydrophobic peptides when their contact angle decreases below θ ≈ 50°-60°, thus confirming the so-called Berg limit established in the context of protein and cell adsorption. Entropy/enthalpy decomposition of the simulation results reveals that the key discriminator between the adsorption of different residues on a hydrophobic monolayer is of entropic nature and thus is suggested to be linked to the hydrophobic effect. By pushing a polyalanine peptide onto a polar surface, simulations reveal that the peptide adsorption resistance is caused by the strongly bound water hydration layer and characterized by the simultaneous gain of both total entropy in the system and total number of hydrogen bonds between water, peptide, and surface. This mechanistic insight into peptide adsorption resistance might help to refine design principles for anti-fouling surfaces

Nanomechanical properties of α-synuclein amyloid fibrils: a comparative study by nanoindentation, harmonic force microscopy, and Peakforce QNM

We report on the use of three different atomic force spectroscopy modalities to determine the nanomechanical properties of amyloid fibrils of the human α-synuclein protein. α-Synuclein forms fibrillar nanostructures of approximately 10 nm diameter and lengths ranging from 100 nm to several microns, which have been associated with Parkinson's disease. Atomic force microscopy (AFM) has been used to image the morphology of these protein fibrils deposited on a flat surface. For nanomechanical measurements, we used single-point nanoindentation, in which the AFM tip as the indenter is moved vertically to the fibril surface and back while the force is being recorded. We also used two recently developed AFM surface property mapping techniques: Harmonic force microscopy (HarmoniX) and Peakforce QNM. These modalities allow extraction of mechanical parameters of the surface with a lateral resolution and speed comparable to tapping-mode AFM imaging. Based on this phenomenological study, the elastic moduli of the α-synuclein fibrils determined using these three different modalities are within the range 1.3-2.1 GPa. We discuss the relative merits of these three methods for the determination of the elastic properties of protein fibrils, particularly considering the differences and difficulties of each method

Single-Molecule Force Spectroscopy: Experiments, Analysis, and Simulations

International audienceThe mechanical properties of cells and of subcellular components are important to obtain a mechanistic molecular understanding of biological processes. The quantification of mechanical resistance of cells and biomolecules using biophysical methods matured thanks to the development of nanotechnologies such as optical and magnetic tweezers, the biomembrane force probe and atomic force microscopy (AFM). The quantitative nature of force spectroscopy measurements has converted AFM into a valuable tool in biophysics. Force spectroscopy allows the determination of the forces required to unfold protein domains and to disrupt individual receptor/ligand bonds. Molecular simulation as a computational microscope allows investigation of similar biological processes with an atomistic detail. In this chapter, we first provide a step-by-step protocol of force spectroscopy including sample preparation, measurement and analysis of force spectroscopy using AFM and its interpretation in terms of available theories. Next, we present the background for molecular dynamics (MD) simulations focusing on steered molecular dynamics (SMD) and the importance of bridging of computational tools with experimental technique

Beyond intima-media-thickness: Analysis of the carotid intima-media-roughness in a paediatric population.

BACKGROUND AND AIMS: Subclinical atherosclerosis assessed by sonographic intima-media-thickness measurement of the carotid artery (cIMT) is considered to be an early precursor of cardiovascular disease already in childhood. Structural analysis of the carotid intimal layer (carotid intima-media-roughness, cIMR) improves cardiovascular risk profiling for the adult patient and has been shown to be increased also in paediatric patients with elevated cardiovascular risk. To date, normal values for the paediatric age are lacking. Thus, we present normative data for a paediatric age group. METHODS: 602 healthy German school children (age 8-18 y) were studied, and cIMT and cIMR calculated; reference values were given for three age groups (group 1: 8-10.99 years; group 2: 11-13.99 years; group 3: 14-17.99 years). RESULTS: cIMT values were: 0.48 ± 0.03 mm for girls and boys in age group 1, 0.49 ± 0.03 mm for girls and boys in age group 2; and 0.45 ± 0.03 mm for girls and 0.49 ± 0.03 mm for boys in age group 3; cIMR was 0.04 ± 0.01 mm for both sexes in age group 1 and 3; while in age group 2, both sexes showed a cIMR of 0.03 ± 0.01 mm. Physical fitness was significantly negatively correlated with cIMR (r = - 0.212, p < 0.0001) and a strong predictor for cIMR increase. CONCLUSIONS: The normative data of cIMR for a paediatric age group presented here allow for the identification of patients at elevated cardiovascular risk. By including cIMR as surface analysis of the arterial wall, the individual risk stratification may be improved compared to thickness-analysis of the Intima-Media-Layer (cIMT) also at a paediatric age

On the Relationship between Peptide Adsorption Resistance and Surface Contact Angle: A Combined Experimental and Simulation Single-Molecule Study

The force-induced desorption of single peptide chains from mixed OH/CH₃-terminated self-assembled monolayers is studied in closely matched molecular dynamics simulations and atomic force microscopy experiments with the goal to gain microscopic understanding of the transition between peptide adsorption and adsorption resistance as the surface contact angle is varied. In both simulations and experiments, the surfaces become adsorption resistant against hydrophilic as well as hydrophobic peptides when their contact angle decreases below θ ≈ 50°–60°, thus confirming the so-called Berg limit established in the context of protein and cell adsorption. Entropy/enthalpy decomposition of the simulation results reveals that the key discriminator between the adsorption of different residues on a hydrophobic monolayer is of entropic nature and thus is suggested to be linked to the hydrophobic effect. By pushing a polyalanine peptide onto a polar surface, simulations reveal that the peptide adsorption resistance is caused by the strongly bound water hydration layer and characterized by the simultaneous gain of both total entropy in the system and total number of hydrogen bonds between water, peptide, and surface. This mechanistic insight into peptide adsorption resistance might help to refine design principles for anti-fouling surfaces