Single Molecule Force Spectroscopy Reveals that Electrostatic Interactions Affect the Mechanical Stability of Proteins

It is well known that electrostatic interactions play important roles in determining the thermodynamic stability of proteins. However, the investigation into the role of electrostatic interactions in mechanical unfolding of proteins has just begun. Here we used single molecule atomic force microscopy techniques to directly evaluate the effect of electrostatic interactions on the mechanical stability of a small protein GB1. We engineered a bi-histidine motif into the force-bearing region of GB1. By varying the pH, histidine residues can switch between protonated and deprotonated states, leading to the change of the electrostatic interactions between the two histidine residues. We found that the mechanical unfolding force of the engineered protein decreased by ∼34% (from 115 pN to 76 pN) on changing the pH from 8.5 to 3, due to the increased electrostatic repulsion between the two positively charged histidines at acidic pH. Our results demonstrated that electrostatic interactions can significantly affect the mechanical stability of elastomeric proteins, and modulating the electrostatic interactions of key charged residues can become a promising method for regulating the mechanical stability of elastomeric proteins

Thickness measurements of graphene oxide flakes using atomic force microscopy:Results of an international interlaboratory comparison

Flake thickness is one of the defining properties of graphene-related 2D materials (GR2Ms), and therefore requires reliable, accurate, and reproducible measurements with well-understood uncertainties. This is needed regardless of the production method or manufacturer because it is important for all GR2M products to be globally comparable. An international interlaboratory comparison on thickness measurements of graphene oxide (GO) flakes using atomic force microscopy (AFM) has been completed in Technical Working Area 41 of Versailles Project on Advanced Materials and Standards (VAMAS). Twelve laboratories participated in the comparison project, led by NIM, China, to improve the equivalence of thickness measurement for two-dimensional flakes. The measurement methods, uncertainty evaluation and a comparison of the results and analysis are reported in this manuscript. The data and results of this project will be directly used to support the development of an ISO standard

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Step height profile along the white line in Data Citation 1-1.  </p

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Values reported by each participant of the average flake thickness from the international.</p

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Step height profile along the white line in Figure 1-1. </p

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Comparison of different analysis programs to measure the thickness of GO flakes.</p

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Participants’ results for GO thickness using different data analysis methods.</p

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Degree of equivalence evaluation of the submitted results. </p