Evolution of Interactions in the Protein Solution As Induced by Mono and Multivalent Ions

Abstract

The evolution of interactions in the bovine serum albumin (BSA) protein solution on addition of mono and multivalent (di, tri and tetra) counterions has been studied using small-angle neutron scattering (SANS), dynamic light scattering (DLS) and ζ-potential measurements. It is found that in the presence of mono and divalent counterions, protein behavior can be well explained by DLVO theory, combining the contributions of screened Coulomb repulsion with the van der Waals attraction. The addition of mono or divalent salts in protein solution reduces the repulsive barrier and hence the overall interaction becomes attractive, but the system remains in one-phase for the entire concentration range of the salts, added in the system. However, contrary to DLVO theory, the protein solution undergoes a reentrant phase transition from one-phase to a two-phase system and then back to the one-phase system in the presence of tri and tetravalent counterions. The results show that tri and tetravalent (unlike mono and divalent) counterions induce short-range attraction between the protein molecules, leading to the transformation from one-phase to two-phase system. The two-phase is characterized by the fractal structure of protein aggregates. The excess condensation of these higher-valent counterions in the double layer around the BSA causes the reversal of charge of the protein molecules resulting into reentrant of the one-phase, at higher salt concentrations. The complete phase behavior with mono and multivalent ions has been explained in terms of the interplay of electrostatic repulsion and ion-induced short-range attraction between the protein molecules.

Boosting the in situ encapsulation of proteins with MIL-100(Fe): the role of strong Lewis acid centers

“…we measured the surface electrostatic potential changes of the model BSA protein upon exposure to divalent (Mg 2+ , Ca 2+ , Zn 2+ and Cu 2+ ) and trivalent (Dy 3+ , La 3+ , Al 3+ and Fe 3+ ) cations. As depicted in Figure 2D, trivalent cations along with Cu 2+ , leaded to drastic changes including inversion of the zeta potential values, in agreement with reported results [65][66][67] . Indeed, exposure to Fe 3+ resulted the most extreme situation and provoked a zeta potential increase of ca.…”

Impact of Arginine–Phosphate Interactions on the Reentrant Condensation of Disordered Proteins

“…The interactions between proteins in solutions are governed by a delicate balance of attractive and repulsive forces. , A range of additives are used to tune the properties of protein solutions, including salt, and small organic molecules such as amino acids. , The addition of salt to protein solutions can also increase protein–protein interactions, resulting in, for example, precipitation, aggregation, or oligomerization. − The precise influence of ionic species on the interactions between proteins in solution is nontrivial and dependent on the concentration and specific properties of both the ion and the protein. , Multivalent ions have been shown to modulate protein–protein interactions when added to solutions of oppositely charged proteins, resulting in rich phase behaviors including re-entrant condensation (RC) and liquid–liquid phase separation. − …”

Multivalent ions and biomolecules: Attempting a comprehensive perspective

“…The inversion of the surface charge is related to a specific phase behaviour called reentrant condensation known from polyelectrolytes (see, e. g., Ref. [260] ), which has been observed in aqueous solutions of negatively charged proteins with trivalent [58,256,261] and tetravalent cations, [262] as illustrated schematically in Figure 5. At a given protein concentration c p and a low salt concentration c s , the system is a homogeneous liquid (Regime I), charge-stabilised by the initially net protein charge.…”