Reentrant Condensation of Proteins in Solution Induced by Multivalent Counterions

Abstract

Negatively charged globular proteins in solution undergo a condensation upon adding trivalent counterions between two critical concentrations C and C, C <C. This reentrant condensation behavior above C is caused by short-ranged electrostatic interactions between multivalent cations and acidic residues, mechanistically different from the case of DNA. Small-angle x-ray scattering indicates a short-ranged attraction between counterion-bound proteins near C and C. Monte Carlo simulations (under these strong electrostatic coupling conditions) support an effective inversion of charge on surface side chains through binding of the multivalent counterions.

Anomalous Protein–Protein Interactions in Multivalent Salt Solution

“…Indeed, a number of SAXS experiments have been performed on protein and trivalent salt systems but the fitting of the spectra has for now been limited to analytical models (screened Coulomb potential and sticky hard spheres). 12,19,20,47 Spectra obtained from many-body simulation would be directly comparable to experimental spectra, and provide further information about the mechanisms underlying the charge reversal. More specifically, such simulations could explicitly include both trivalent ions and protein counter-ions while monovalent ions are included implicitly, which would account for the influence of counter-ion condensation on protein-protein interactions.…”

“…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.…”

“…3,4 This has been observed for a variety of macromolecules and ions, such as latex particles, polyelectrolytes, DNA, proteins, multivalent ions and surfactant micelles. [4][5][6][7][8][9][10][11][12][13] The mechanism relies mainly on strong spatial correlations between ions adsorbed at the surface of the macromolecule, a feature which is not taken into account by generic mean-field theories. [1][2][3][14][15][16] Human Serum Albumin (HSA) is a 585 residues long, 66.5 kDa protein, which is involved in the transport of diverse molecules in blood plasma.…”

“…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.…”

Single chain contraction and re-expansion of polystyrene sulfonate: A study on its re-entrant condensation at single molecular level

“…The phenomenon is observed as the precipitation of the solute in aqueous solution upon the addition of multivalent salts up to a critical amount, and the precipitation redissolves into the solution when the salt concentration is further elevated beyond another value. Such a phenomenon involves almost every kind of soft matter systems carrying charges, including biomacromolecules such as DNA 1-5 and protein, [6][7][8] charged polymers such as polyelectrolytes, [9][10][11][12][13][14] as well as colloidal particles. 15 The mystery of re-entrant condensation has been attracting intensive research interests for decades.…”