Coarse-grained modelling of the intrinsically disordered protein Histatin 5 in solution. Monte Carlo simulations in combination with SAXS.

Monte Carlo simulations and coarse-grained modelling have been used to analyze Histatin 5, which is an unstructured short cationic salivary peptide known to have anti-candidical properties. The calculated scattering functions have been compared with intensity curves and the distance distribution function P(r) obtained from SAXS, at both high and low salt concentrations. The aim is to achieve a molecular understanding and a physico-chemical insight of the obtained SAXS results and to gain information of conformational changes of Histatin 5 due to altering salt content, charge distribution, and net charge. From a modelling perspective, the accuracy of the electrostatic interaction is of special interest. The used coarse-grained model is based on the primitive model in which charged hard spheres differing in charge and in size represent the ionic particles, and the solvent only enters the model through its relative permittivity. The Hamiltonian of the model comprises three different contributions: (i) excluded volumes, (ii) electrostatic, and (iii) van der Waals interactions. Even though the model can be considered as gross omitting atomistic details, a great correspondence is obtained with experimental results. This article is protected by copyright. All rights reserved.