Effects of Ionic Strength on the Morphology, Scattering, and Mechanical Response of Neurofilament-Derived Protein Brushes

TL;DR

This study uses a theoretical model to analyze how ionic strength influences the structure, scattering, and mechanical properties of neurofilament-derived protein brushes, revealing distinct morphological regimes and their experimental signatures.

Contribution

It introduces a coarse-grained self-consistent field theory model that predicts morphological regimes of protein brushes under varying ionic strengths, aligning with experimental observations.

Findings

Identification of three morphological regimes: swollen, condensed, and coexisting brushes.

Prediction of brush height changes consistent with experimental data across ionic strengths.

Correlation of scattering and mechanical response features with specific brush morphologies.

Abstract

Protein brushes not only play a key role in the functionality of neurofilaments but also have wide applications in biomedical materials. Here, we investigate the effect of ionic strength on the morphology of protein brushes using a continuous-space self-consistent field theory. A coarse-grained multi-block charged macromolecular model is developed to capture the chemical identity of amino acid sequences. For neurofilament heavy (NFH) brushes at pH 2.4, we predict three morphological regimes: swollen brushes, condensed brushes, and coexisting brushes which consist of both a dense inner layer and a diffuse outer layer. The brush height predicted by our theory is in good agreement with experimental data for a wide range of ionic strengths. The dramatic height decrease is a result of the electrostatic screening-induced transition from the overlapping state to the isolated state of the coexisting brushes. We also study the evolution of the scattering and mechanical responses accompanying the morphological change. The oscillation in the reflectivity spectra characterizes the existence and microstructure of the inner condensed layer, whereas the shoulder in the force spectra signifies the swollen morphology.