Influence of Calcium Binding on Conformations and Motions of Anionic Polyamino Acids. Effect of Side Chain Length

Dmitry Tolmachev; Natalia Lukasheva; George Mamistvalov; Mikko Karttunen

doi:10.3390/polym12061279

Influence of Calcium Binding on Conformations and Motions of Anionic Polyamino Acids. Effect of Side Chain Length

Polymers (Basel). 2020 Jun 3;12(6):1279. doi: 10.3390/polym12061279.

Authors

Dmitry Tolmachev¹, Natalia Lukasheva¹, George Mamistvalov², Mikko Karttunen^{1

3

4

5}

Affiliations

¹ Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoy pr. 31, 199004 St. Petersburg, Russia.
² Faculty of Physics, St. Petersburg State University, Petrodvorets, 198504 St. Petersburg, Russia.
³ Department of Chemistry, the University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada.
⁴ Department of Applied Mathematics, the University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada.
⁵ The Centre of Advanced Materials and Biomaterials Research, the University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada.

Abstract

Investigation of the effect of CaCl₂ salt on conformations of two anionic poly(amino acids) with different side chain lengths, poly-(α-l glutamic acid) (PGA) and poly-(α-l aspartic acid) (PASA), was performed by atomistic molecular dynamics (MD) simulations. The simulations were performed using both unbiased MD and the Hamiltonian replica exchange (HRE) method. The results show that at low CaCl₂ concentration adsorption of Ca²⁺ ions lead to a significant chain size reduction for both PGA and PASA. With the increase in concentration, the chains sizes partially recover due to electrostatic repulsion between the adsorbed Ca²⁺ ions. Here, the side chain length becomes important. Due to the longer side chain and its ability to distance the charged groups with adsorbed ions from both each other and the backbone, PGA remains longer in the collapsed state as the CaCl₂ concentration is increased. The analysis of the distribution of the mineral ions suggests that both poly(amino acids) should induce the formation of mineral with the same structure of the crystal cell.

Keywords: Hamiltonian replica exchange; mineralization; molecular dynamic simulation; poly(amino acids); poly-(α-l aspartic acid); poly-(α-l glutamic acid); salt solutions.

Abstract

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