Effects of pH and Salt Concentration on Stability of a Protein G Variant Using Coarse-Grained Models

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Martins de Oliveira, Vinícius [UNESP]
Godoi Contessoto, Vinícius de [UNESP]
Bruno da Silva, Fernando [UNESP]
Zago Caetano, Daniel Lucas [UNESP]
Jurado de Carvalho, Sidney [UNESP]
Pereira Leite, Vitor Barbanti [UNESP]

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The importance of charge-charge interactions in the thermal stability of proteins is widely known. pH and ionic strength play a crucial role in these electrostatic interactions, as well as in the arrangement of ionizable residues in each protein-folding stage. In this study, two coarse-grained models were used to evaluate the effect of pH and salt concentration on the thermal stability of a protein G variant (1PGB-QDD), which was chosen due to the quantity of experimental data exploring these effects on its stability. One of these coarse-grained models, the TKSA, calculates the electrostatic free energy of the protein in the native state via the Tanford-Kirkwood approach for each residue. The other one, CpHMD-SBM, uses a Coulomb screening potential in addition to the structure-based model Cα. Both models simulate the system in constant pH. The comparison between the experimental stability analysis and the computational results obtained by these simple models showed a good agreement. Through the TKSA method, the role of each charged residue in the protein's thermal stability was inferred. Using CpHMD-SBM, it was possible to evaluate salt and pH effects throughout the folding process. Finally, the computational pKa values were calculated by both methods and presented a good level of agreement with the experiments. This study provides, to our knowledge, new information and a comprehensive description of the electrostatic contribution to protein G stability.



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Biophysical Journal, v. 114, n. 1, p. 65-75, 2018.