Study on the thermodynamics of bovine serum albumin aqueous solutions: experiments, modeling and molecular simulations.

Author(s)

Luís Fernando Mercier Franco

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2015-11-27

Examining board members

Pedro de Alcantara Pessoa Filho; Charlles Rubber de Almdeida Abreu; Marcelo Castier; Edward Joseph Maginn; Everson Alves Miranda

• Advisor: Pedro de Alcantara Pessoa Filho

Abstract

The interaction between two proteins into salt aqueous solutions is investigated throughout this thesis. Experiments, modeling and molecular simulations were carried out to get a better understanding of the phenomenon. Bovine serum albumin was used as a model protein. An analytical expression for the structure factor for globular proteins in aqueous solution is presented in this work. This expression was obtained considering an intermolecular potential given by the sum of a hard core, a van der Waals attractive and a screened Coulomb contribution. Experimental data of Small Angle X-Ray Scattering for bovine serum albumin in aqueous solutions containing sodium salts at different protein concentrations and pH values are also presented. The expression developed for the structure factor describes accurately these experimental data provided a dependence of the attractive parameter on protein concentration is established. An expression for the osmotic pressure was derived from the structure factor. With attractive parameters adjusted from X-ray scattering data, the osmotic pressure of bovine serum albumin aqueous solutions could be predicted with very good agreement with experimental data. A derivation of the thermodynamic potentials, such as the chemical potential, using the new osmotic equation of state is presented. Applying the phase equilibrium criterion, the fluid-fluid phase equilibrium for bovine serum albumin in salt aqueous solution was calculated. Although such separation was not experimentally observed at the isoelectric point, it was indeed experimentally observed for a pH value below the isoelectric point. The predictions seem to be valuable to discuss how ion specificity affects the phase diagram of proteins. To apply molecular dynamic techniques to simulate how proteins interact to each other in salt aqueous solutions, two new coarse-grained force fields are proposed. The first one, meant for sodium sulfate aqueous solution, avoids the unphysical association observed for non-polarizable atomistic force fields; and allows the prediction of thermodynamic and dynamic properties. The second one, meant for bovine serum albumin in aqueous solution, is used as a new strategy to evaluate the scattering form factor of proteins as a low resolution technique for protein structure prediction. (AU)

• FAPESP's process: 11/22070-5 - Thermodynamics of protein solutions: experimental determination and modeling of protein-protein interactions
• Grantee: Luís Fernando Mercier Franco
• Support Opportunities: Scholarships in Brazil - Doctorate