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Blanco PM, Achetoni MM, Garcés JL, Madurga S, Mas F, Baieli MF, Narambuena CF. Adsorption of flexible proteins in the 'wrong side' of the isoelectric point: Casein macropeptide as a model system. Colloids Surf B Biointerfaces 2022; 217:112617. [PMID: 35738075 DOI: 10.1016/j.colsurfb.2022.112617] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 04/10/2022] [Accepted: 06/06/2022] [Indexed: 01/05/2023]
Abstract
We analyze the conditions of the adsorption of a flexible peptide onto a charged substrate in the 'wrong side' of the isoelectric point (WSIP), i.e. when surface and peptide charges have the same sign. As a model system, we focus on the casein macropeptide (CMP), both in the aglycosylated (aCMP) and fully glycosydated (gCMP) forms. We model the substrate as a uniformly charged plane while CMP is treated as a bead-and-spring model including electrostatic interactions, excluded volume effects and acid/base equilibria. Adsorption coverage, aminoacid charges and concentration profiles are computed by means of Monte Carlo simulations at fixed pH and salt concentration. We conclude that for different reasons the CMP can be adsorbed to both positively and negatively charged surfaces in the WSIP. For negatively charged surfaces, WSIP adsorption is due to the patchy distribution of charges: the peptide is attached to the surface by the positively charged end of the chain, while the repulsion of the surface for the negatively charged tail is screened by the small ions of the added salt. This effect increases with salt concentration. Conversely, a positively charged substrate induces strong charge regulation of the peptide: the acidic groups are deprotonated, and the peptide becomes negatively charged. This effect is stronger at low salt concentrations and it is more intense for gCMP than for aCMP, due to the presence of the additional sialic groups in gCMP.
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Affiliation(s)
- Pablo M Blanco
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 00 Prague 2, Czech Republic; Department of Material Science and Physical Chemistry & Institute of Theoretical and Computational Chemistry (IQTC), University of Barcelona, C/ Martí i Franquès, 1, 08028 Barcelona, Catalonia, Spain
| | - Micaela M Achetoni
- Universidad Tecnología Nacional & Grupo Bionanotecnología y Sistemas Complejos. (UTN-CONICET), Facultad Regional San Rafael, Av. General Urquiza 314C.P.:5600, San Rafael, Mendoza, Argentina
| | - Josep L Garcés
- Department of Chemistry, University of Lleida, Av. Alcalde Rovira Roure 191, E-25198 Lleida, Catalonia, Spain
| | - Sergio Madurga
- Department of Material Science and Physical Chemistry & Institute of Theoretical and Computational Chemistry (IQTC), University of Barcelona, C/ Martí i Franquès, 1, 08028 Barcelona, Catalonia, Spain
| | - Francesc Mas
- Department of Material Science and Physical Chemistry & Institute of Theoretical and Computational Chemistry (IQTC), University of Barcelona, C/ Martí i Franquès, 1, 08028 Barcelona, Catalonia, Spain
| | - María F Baieli
- Universidad de Buenos Aires & Instituto de Nanobiotecnología (UBA-CONICET), Facultad de Farmacia y Bioquímica, Buenos Aires, Argentina
| | - Claudio F Narambuena
- Universidad Tecnología Nacional & Grupo Bionanotecnología y Sistemas Complejos. (UTN-CONICET), Facultad Regional San Rafael, Av. General Urquiza 314C.P.:5600, San Rafael, Mendoza, Argentina.
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Blanco PM, Madurga S, Garcés JL, Mas F, Dias RS. Influence of macromolecular crowding on the charge regulation of intrinsically disordered proteins. SOFT MATTER 2021; 17:655-669. [PMID: 33215185 DOI: 10.1039/d0sm01475c] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In this work we study the coupling between ionization and conformational properties of two IDPs, histatin-5 and β-amyloid 42, in the presence of neutral and charged crowders. The latter is modeled to resemble bovine serum albumin (BSA). With this aim, semi-grand canonical Monte Carlo simulations are performed, so that the IDP charge is a dynamic property, undergoing protonation/deprotonation processes. Both ionization properties (global and specific amino acid charge and binding capacitance) and radius of gyration are analyzed in a large range of pH values and salt concentrations. Without crowder agents, the titration curve of histatin-5, a polycation, is salt-dependent while that of β-amyloid 42, a polyampholyte, is almost unaffected. The salt concentration is found to be particularly relevant at pH values where the protein binding capacitance (directly linked with charge fluctuation) is larger. Upon addition of neutral crowders, charge regulation is observed in histatin-5, while for β-amyloid 42 this effect is very small. The main mechanism for charge regulation is found to be the effective increase in the ionic strength due to the excluded volume. In the presence of charged crowders, a significant increase in the charge of both IDPs is observed in almost all the pH range. In this case, the IDP charge is altered not only by the increase in the effective ionic strength but also by its direct electrostatic interaction with the charged crowders.
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Affiliation(s)
- Pablo M Blanco
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona, Catalonia, Spain.
| | - Sergio Madurga
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona, Catalonia, Spain.
| | - Josep L Garcés
- Chemistry Department, Technical School of Agricultural Engineering & AGROTECNIO of Lleida University (UdL), Lleida, Catalonia, Spain
| | - Francesc Mas
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona, Catalonia, Spain.
| | - Rita S Dias
- Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
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Non-monotonic behavior of weak-polyelectrolytes adsorption on a cationic surface: A Monte Carlo simulation study. POLYMER 2021. [DOI: 10.1016/j.polymer.2020.123170] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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PDADMAC/PSS Oligoelectrolyte Multilayers: Internal Structure and Hydration Properties at Early Growth Stages from Atomistic Simulations. Molecules 2020; 25:molecules25081848. [PMID: 32316422 PMCID: PMC7222011 DOI: 10.3390/molecules25081848] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 04/06/2020] [Accepted: 04/14/2020] [Indexed: 11/17/2022] Open
Abstract
We analyze the internal structure and hydration properties of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) oligoelectrolyte multilayers at early stages of their layer-by-layer growth process. Our study is based on large-scale molecular dynamics simulations with atomistic resolution that we presented recently [Sánchez et al., Soft Matter2019, 15, 9437], in which we produced the first four deposition cycles of a multilayer obtained by alternate exposure of a flat silica substrate to aqueous electrolyte solutions of such polymers at 0.1M of NaCl. In contrast to any previous work, here we perform a local structural analysis that allows us to determine the dependence of the multilayer properties on the distance to the substrate. We prove that the large accumulation of water and ions next to the substrate observed in previous overall measurements actually decreases the degree of intrinsic charge compensation, but this remains as the main mechanism within the interface region. We show that the range of influence of the substrate reaches approximately 3 nm, whereas the structure of the outer region is rather independent from the position. This detailed characterization is essential for the development of accurate mesoscale models able to reach length and time scales of technological interest.
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Mella M, Tagliabue A, Mollica L, Izzo L. Monte Carlo study of the effects of macroion charge distribution on the ionization and adsorption of weak polyelectrolytes and concurrent counterion release. J Colloid Interface Sci 2020; 560:667-680. [PMID: 31704002 DOI: 10.1016/j.jcis.2019.10.051] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Revised: 10/12/2019] [Accepted: 10/14/2019] [Indexed: 01/16/2023]
Abstract
HYPOTHESIS Adsorption of weak polyelectrolytes onto charged nanoparticles, and concurrent effects such as spatial partitioning of ions may be influenced by details of the polyelectrolyte structure (linear or star-like) and size, by the mobility of the nanoparticle surface charge, or the valence of the nanoparticle counterions. EXPERIMENTS Ionization and complexation of weak polyelectrolytes on spherical macroions with monovalent and divalent countrions has been studied with constant-pH Monte Carlo titrations and primitive electrolyte models for linear and star-like polymers capable, also, of forming charged hydrogen bonds. Nanoparticles surface charge has been represented either as a single colloid-centered total charge (CCTC) or as surface-tethered mobile monovalent spherical charges (SMMSC). FINDINGS Differences in the average number of adsorbed polyelectrolyte arms and their average charge, and in the relative amount of macroion counterions (m-CI's) released upon polymer adsorption are found between CCTC and SMMSC nanoparticles. The amount of the counterions released also depends on the polymer structure. As CCTC adsorbs a lower number of star-like species arms, the degree of condensation of polymer counterions (p-CI's) onto the polyelectrolyte is also substantially higher for the CCTC colloid, with a concurrent decrease of the osmotic coefficient values.
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Affiliation(s)
- Massimo Mella
- Dipartimento di Scienza ed Alta Tecnologia, Università degli Studi dell'Insubria, via Valleggio 11, 22100 Como, Italy.
| | - Andrea Tagliabue
- Dipartimento di Scienza ed Alta Tecnologia, Università degli Studi dell'Insubria, via Valleggio 11, 22100 Como, Italy
| | - Luca Mollica
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università degli Studi di Milano, via Vanvitelli 32, 20133 Milano, Italy; Istituto Nazionale Genetica Molecolare "Romeo ed Enrica Invernizzi", Via F. Sforza 35, 20122 Milano, Italy
| | - Lorella Izzo
- Dipartimento di Biotecnologie e Scienze della Vita, Università degli Studi dell'Insubria, via J. H. Dunant 3, 21100 Varese, Italy.
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Sánchez PA, Vögele M, Smiatek J, Qiao B, Sega M, Holm C. Atomistic simulation of PDADMAC/PSS oligoelectrolyte multilayers: overall comparison of tri- and tetra-layer systems. SOFT MATTER 2019; 15:9437-9451. [PMID: 31720676 DOI: 10.1039/c9sm02010a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
By employing large-scale molecular dynamics simulations of atomistically resolved oligoelectrolytes in aqueous solutions, we study in detail the first four layer-by-layer deposition cycles of an oligoelectrolyte multilayer made of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) (PDADMAC/PSS). The multilayers are grown on a silica substrate in 0.1 M NaCl electrolyte solutions and the swollen structures are then subsequently exposed to varying added salt concentration. We investigated the microscopic properties of the films, analyzing in detail the differences between three- and four-layer systems. Our simulations provide insights into the early stages of growth of a multilayer, which are particularly challenging for experimental observations. We found rather strong complexation of the oligoelectrolytes, with fuzzy layering of the film structure. The main charge compensation mechanism is for all cases intrinsic, whereas extrinsic compensation is relatively enhanced for the layer of the last deposition cycle. In addition, we quantified other fundamental observables of these systems, such as the film thickness, water uptake, and overcharge fractions for each deposition layer.
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Affiliation(s)
- Pedro A Sánchez
- Ural Federal University, 51 Lenin av., Ekaterinburg, 620000, Russian Federation. and Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden, Germany
| | - Martin Vögele
- Department of Computer Science, Stanford University, Stanford, California, USA
| | - Jens Smiatek
- Institut für Computerphysik, Universität Stuttgart, 70569 Stuttgart, Germany
| | - Baofu Qiao
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois, USA
| | - Marcello Sega
- Forschungszentrum Jülich, Helmholtz Institute Erlangen-Nuremberg, Nuremberg, Germany
| | - Christian Holm
- Institut für Computerphysik, Universität Stuttgart, 70569 Stuttgart, Germany
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Narambuena CF. On the reasons for α-lactalbumin adsorption on a charged surface: a study by Monte Carlo simulation. Colloids Surf B Biointerfaces 2019; 174:511-520. [PMID: 30497013 DOI: 10.1016/j.colsurfb.2018.11.056] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 11/03/2018] [Accepted: 11/20/2018] [Indexed: 12/26/2022]
Abstract
This work studies α-lactalbumin adsorption on a charged substrate using Monte Carlo simulation. The protein is represented by a coarse-grained model with enough components as to reproduce the complex behavior of α-lactalbumin on electrically-charged substrates. The simulation results in particular can reproduce protein adsorption when both the protein and the substrate are negatively charged. The energetic and entropic contributions to the free energy of the adsorption process are estimated and analyzed. The effects of the charge regulation mechanism, the localization of titratable groups in α-lactalbumin as well as the distribution of small ions around the interface are studied in detail. Both the asymmetrical distribution of the charged groups of the protein and the counterion distribution play predominant roles in α-lactalbumin adsorption on a substrate with the same sign of electrical charge.
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Affiliation(s)
- Claudio F Narambuena
- Facultad Regional San Rafael, Universidad Tecnológica Nacional, San Rafael, Mendoza, Argentina; Instituto de Física Aplicada CONICET-UNSL, San Luis, Argentina.
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Sergeeva IP, Sobolev VD. The Effect of Surface Charge on Adsorption of a Cationic Polyelectrolyte. COLLOID JOURNAL 2018. [DOI: 10.1134/s1061933x18010106] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Behavior of a Weak Polyelectrolyte at Oil-water Interfaces under Different Environmental Conditions. Colloids Surf A Physicochem Eng Asp 2018. [DOI: 10.1016/j.colsurfa.2017.11.029] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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