Issue 35, 2016

Modeling phase transitions in mixtures of β–γ lens crystallins

Abstract

We analyze the experimentally determined phase diagram of a γD–βB1 crystallin mixture. Proteins are described as dumbbells decorated with attractive sites to allow inter-particle interaction. We use thermodynamic perturbation theory to calculate the free energy of such mixtures and, by applying equilibrium conditions, also the compositions and concentrations of the co-existing phases. Initially we fit the Tcloudversus packing fraction η measurements for a pure (x2 = 0) γD solution in 0.1 M phosphate buffer at pH = 7.0. Another piece of experimental data, used to fix the model parameters, is the isotherm x2vs. η at T = 268.5 K, at the same pH and salt content. We use the conventional Lorentz–Berthelot mixing rules to describe cross interactions. This enables us to determine: (i) model parameters for pure βB1 crystallin protein and to calculate; (ii) complete equilibrium surface (Tcloudx2η) for the crystallin mixtures. (iii) We present the results for several isotherms, including the tie-lines, as also the temperature-packing fraction curves. Good agreement with the available experimental data is obtained. An interesting result of these calculations is evidence of the coexistence of three phases. This domain appears for the region of temperatures just out of the experimental range studied so far. The input parameters, leading good description of experimental data, revealed a large difference between the numbers of the attractive sites for γD and βB1 proteins. This interesting result may be related to the fact that γD has a more than nine times smaller quadrupole moment than its partner in the mixture.

Graphical abstract: Modeling phase transitions in mixtures of β–γ lens crystallins

Supplementary files

Article information

Article type
Paper
Submitted
01 Jul 2016
Accepted
01 Aug 2016
First published
01 Aug 2016
This article is Open Access
Creative Commons BY license

Soft Matter, 2016,12, 7289-7298

Author version available

Modeling phase transitions in mixtures of β–γ lens crystallins

M. Kastelic, Y. V. Kalyuzhnyi and V. Vlachy, Soft Matter, 2016, 12, 7289 DOI: 10.1039/C6SM01513A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements