Universality of protein reentrant condensation in solution induced by multivalent metal ions

Abstract

The effective interactions and phase behavior of protein solutions under strong electrostatic coupling conditions are difficult to understand due to the complex charge pattern and irregular geometry of protein surfaces. This distinguishes them from related systems such as DNA or conventional colloids. In this work, we discuss the question of universality of the reentrant condensation (RC) of proteins in solution induced by multivalent counterions, i.e., redissolution on adding further salts after phase separation, as recently discovered (Zhang et al., Phys Rev Lett 2008; 101:148101). The discussion is based on a systematic investigation of five different proteins with different charge patterns and five different multivalent counterions. Zeta potential measurements confirm the effective charge inversion of proteins in the reentrant regime via binding of multivalent counterions, which is supported by Monte Carlo simulations. Charge inversion by trivalent cations requires an overall negative net charge of the protein. Statistical analysis of a representative set of protein sequences reveals that, in theory, this effect could be possible for about half of all proteins. Our results can be exploited for the control of the phase behavior of proteins, in particular facilitating protein crystallization.

Anomalous Protein–Protein Interactions in Multivalent Salt Solution

“…This work, at a microscopic level, echoes experimental results showing the existence of reentrant condensation in HSA solutions in the presence of trivalent ions [18][19][20] and is also in agreement with recent calorimetry experiments. 45 Different models were used: an atomic model, a coarse-grained model, and a colloidal The colloidal model was used to study the interactions of two spherical colloids representing HSA-like molecules.…”

“…The above results correlate well with the reentrant condensation of HSA in the presence of yttrium reported in the litterature. 12,18,23 Indeed, the increase in YCl 3 concentration first causes a reduction of the absolute value of the net charge of HSA molecules, decreasing inter-particle repulsion and promoting inter-particle attraction, whereafter the net charge of the HSA molecules reverses and its absolute value increases, causing renewed repulsion.…”

“…17 HSA solutions undergo reentrant condensation upon addition of trivalent salts (YCl 3 , LaCl 3 , FeCl 3 , or AlCl 3 ). [18][19][20] That is, upon increase of the trivalent salt concentration, protein aggregation is first observed, then redissolution of the samples occurs. This anomalous trend, caused by charge reversal, has been shown to be able to induce clustering, liquid-liquid phase separation or crystallization.…”

“…This anomalous trend, caused by charge reversal, has been shown to be able to induce clustering, liquid-liquid phase separation or crystallization. 12,18,[21][22][23][24][25] The ability to control the phase behavior of protein dispersions show promising opportunities, for example for the production of high quality protein crystals, required for protein structure determination.…”

Viscosity and diffusion: crowding and salt effects in protein solutions

“…For example, it has been shown that surface patchiness has an important effect on the phase diagram [11]. Also, binding of multivalent ions to the protein surface can give rise to non mean-field behaviors beyond DLVO, such as charge inversion, re-entrant condensation and liquid-liquid phase separation [12][13][14].…”