Both Charge-Regulation and Charge-Patch Distribution Can Drive Adsorption on the Wrong Side of the Isoelectric Point

Abstract

The mechanism of protein–polyelectrolyte complexation on the wrong side of the isoelectric point has long puzzled researchers. Two alternative explanations have been proposed in the literature: (a) the charge-patch (CP) mechanism, based on the inhomogeneous distribution of charges on the protein, and (b) the charge-regulation (CR) mechanism, based on the variable charge of weak acid and base groups, which may invert the protein charge in the presence of another highly charged object. To discern these two mechanisms, we simulated artificially constructed short peptides, containing acidic and basic residues, arranged in a blocklike or alternating sequence. Our simulations of these peptides, interacting with polyelectrolytes, showed that charge patch and charge regulation alone can both lead to adsorption on the wrong side of the pI value. Their simultaneous presence enhances adsorption, whereas their absence prevents adsorption. Our simulation results were rationalized by following the variation of the charge regulation capacity and dipole moments of these peptides with the pH. Specifically for lysozyme, we found that charge patch prevails at physiological pH, whereas charge regulation prevails near the pI, thereby explaining seemingly contradicting conclusions in the literature. By applying the same approach to other proteins, we developed a general framework for assessing the role of the CP and CR mechanisms in existing case studies and for predicting how various proteins interact with polyelectrolytes at different pH values.

Electrostatic features for the Receptor binding domain of SARS-COV-2 wildtype and its variants. Compass to the severity of the future variants with the charge-rule

“…In doing so, the electrostatic interactions are fully described by this simple and robust model. The charge regulation mechanism that can result in additional mesoscopic attractive electrostatic forces 68,69,91 is properly incorporated. Non-titratable amino acids are kept neutral all the time.…”

“…Here, pH is an input parameter as is the temperature). 66 This implies that possible contributions from mesoscopic electrostatic mechanisms as the charge regulation phenomena due to the proton fluctuations [67][68][69] were not considered and/or quantified in many previous works. Similarly, calculations were performed almost exclusively at pH 7.…”

Self-association features of NS1 proteins from different flaviviruses

“…At pHs conditions closer to 7, NS1 ZIKV-UG and NS1 ZIKV-BR in the dimeric states have a particular characteristic presenting higher dipole values than the remaining NS1 flavivirus . These observations indicate that charge regulation and dipole interactions (Barroso da Silva et al, 2006; Da Silva and Jönsson, 2009; Lunkad et al, 2022) can play a more important and specific role for each viral system when the salt concentration is sufficiently low.…”

“…Only titration was included as an MC movement in these runs. The FPTS was employed at a different pH condition from 0.1 to 14 every 0.1 pH unit to compute the corresponding protein net charge number ( Z P ), the charge regulation capacity ( C P ), and the dipole moment number ( μ P ) as previously proposed (Delboni and Da Silva, 2016; Jonsson and Lund, 2007; Lunkad et al, 2022; Poveda-Cuevas et al, 2018). For the other simulation sets where the focus was on the complexation process, much longer and quite expensive (in terms of CPU time) simulations were necessary.…”

Biomolecular Complexation on the “Wrong Side”: A Case Study of the Influence of Salts and Sugars on the Interactions between Bovine Serum Albumin and Sodium Polystyrene Sulfonate

“…An alternative mechanism to the charge-patch mechanism used in the literature to explain the complexation on the "wrong side" is the so-called charge-regulation mechanism. Although the two mechanisms (charge-patch and charge-regulation) are not mutually exclusive, as recently shown by Lunkand et al, 62 the ability of BSA to chargeregulate at pH ≈ 8.0 is low. 25 In addition, charge regulation is usually considered at low ionic strengths (a few mM), and bearing in mind that we performed our measurements at larger ionic strengths (I total = 20 mM), the association between NaPSS and BSA at pH = 8.0, where BSA also has a large dipole moment, 63,64 is most likely a consequence of the charge-patch mechanism.…”