Proton-Coupled Protein Binding: Controlling Lysozyme/Poly(acrylic acid) Interactions with pH

Insights into the Mechanism of Protein Loading by Chain-Length Asymmetric Complex Coacervates

The study of the phase behavior of polyelectrolyte complex coacervates has attracted significant attention in recent years due to their potential use as membrane-less organelles, microreactors, and drug delivery platforms. In this work, we investigate the mechanism of protein loading in chain-length asymmetric complex coacervates composed of a polyelectrolyte and an oppositely charged multivalent ion. Unlike the symmetric case (polycation + polyanion), we show that protein loading is highly selective based on the protein's net charge: only proteins with charges opposite to the polyelectrolyte can be loaded. Through a series of systematic experiments, we identified that the protein loading process relies on the formation of a neutral three-component coacervate in which both the protein and the multivalent ion serve as complexing agents for the polyelectrolyte. Lastly, we demonstrated that this mechanism extends to the sequestration of other charged small molecules, offering valuable insights into designing functional multicomponent coacervates.

Polymers for Disrupting Protein-Protein Interactions: Where Are We and Where Should We Be?

Protein-protein interactions (PPIs) are central to the cellular signaling and regulatory networks that underlie many physiological and pathophysiological processes. It is challenging to target PPIs using traditional small molecule or peptide-based approaches due to the frequent lack of well-defined binding pockets at the large and flat PPI interfaces. Synthetic polymers offer an opportunity to circumvent these challenges by providing unparalleled flexibility in tuning their physiochemical properties to achieve the desired binding properties. In this review, we summarize the current state of the field pertaining to polymer-protein interactions in solution, highlighting various polyelectrolyte systems, their tunable parameters, and their characterization. We provide an outlook on how these architectures can be improved by incorporating sequence control, foldability, and machine learning to mimic proteins at every structural level. Advances in these directions will enable the design of more specific protein-binding polymers and provide an effective strategy for targeting dynamic proteins, such as intrinsically disordered proteins.

Effect of pH on the Poly(acrylic acid)/Poly(vinyl alcohol)/Lysozyme Complexes Formation

The interactions between poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), and lysozyme (Lys) in an aqueous environment at pHs of 2, 4, and 7.4 were discussed considering the experimental data obtained by turbidimetry, electrokinetic and rheological measurements, and FTIR analysis. It was found that the increase in PAA amount reduces the coacervation zone by shifting the critical pHcr1to higher values while the critical pHcr2 remains unchanged. The coacervation zone extended from 3.1-4.2 to 2.9-4.7 increasing the Lys concentration from 0.2% to 0.5%. The zeta potential measurements showed that the PAA-PVA-Lys mixture in water is the most stable in the pH range of 4.5-8. Zero shear viscosity exhibited deviations from additivity at both investigated pHs, and a maximum value corresponding to a maximum hydrodynamic volume was revealed at PAA weight fractions of 0.4 and 0.5 for pHs of 4 and 7.4, respectively. The binding affinity to Lys of PAA, established by molecular dynamics simulation, was slightly higher than that of PVA. The more stable complex was PAA-Lys formed in a very acidic environment; for that, a binding affinity of -7.1 kcal/mol was determined.

Interaction between whey protein and soy lecithin and its influence on physicochemical properties and in vitro digestibility of emulsion: A consideration for mimicking milk fat globule

In this study, from the perspective of simulating the milk fat globule (MFG) emulsion, the interaction between soybean lecithin (SL) and the main protein in milk, whey protein (WP), and its effect on physical characteristics and lipid digestion were investigated through multiple spectroscopic techniques and in vitro digestion. The mechanism of SL and WP was static quenching, indicating that a complex formed between WP and SL through hydrophobic interaction and hydrogen bonding. The addition of SL changed the secondary structure of WP. When the ratio of SL to WP was 1:3, the obtained SL-WP emulsion that simulated milk fat globule exhibited the smallest particle size distribution and the highest absolute value of zeta potential. In addition, the emulsion exhibited high encapsulation efficiency (91.67 ± 1.24 %) and good stability. Compared with commercially available infant formula (IF), the final free fatty acid release of prepared SL-WP emulsion was close to that of human milk (HM). The addition of lecithin increased the digestibility of fat and the release of free fatty acids, and the digestive characteristic and particle size change also were closer to that of HM from results of kinetics of free fatty acid release and microstructure analysis.

Polystyrene@poly(ar-vinylbenzyl)trimethylammonium-co-acrylic acid core/shell pH-responsive nanoparticles for active targeting and imaging of cancer cell based on aggregation induced emission

Doubly charged pH-responsive core/shell hydrogel nanoparticles with green fluorescence were prepared and were shown to be viable bioprobes for active targeting tumor tissue and imaging of cancer cells. Via emulsionfree copolymerization hydrogel nanoparticles as VANPs were prepared, the core of which was polystyrene (Ps) and the shell was comprised of strongly positive electrolyte (ar-vinylbenzyl)trimethylammonium (VBTAC) with weak negative electrolyte acrylic acid (AA). Through conventional amidation, the shell was conjugated with cell-specific folic acid (FA), denoted as VANPs-FA. Then, negatively charged sulfonated 9,10-distyrylanthracene derivatives (SDSA) based on aggregation induced emission (AIE), was binding tightly to positively charged VBTAC of VANPs-FA shell. The prepared double charged fluorescent core/shell hydrogel nanoparticles abbreviated as VANPs-FS, showed excitation/emission wavelengths at ~420/528 nm. Dynamic light scattering (DLS) measurements were performed to determine the size and surficial zeta potential of VANPs-FS. Under proper ratio of VBTAC to AA, the VANPs-FS was stable (~ 64.63 nm, -20.2 mV) at high pH (> 7), started to aggregate (~ 683.0 nm, -3.2 mV) at pH around 6, and can redispers at low pH (< 5). The MTT analysis proved that VANPs-FS had good biocompatibility and low cytotoxicity. The targeting effectiveness of VANPs-FS was confirmed by confocal laser scanning microscopy (CLSM). Graphical abstract Detailed synthetic route of VANPs-FS (top) and schematic cancer tumor-target aggregation of pH-sensitive VANPs-FS with enhanced retention and rapid cancer cell imaging (bottom).

Nanogels of carboxymethyl chitosan and lysozyme encapsulated amorphous calcium phosphate to occlude dentinal tubules

This study aimed to develop of a rapid and effective method to occlude dentinal tubules using carboxymethyl chitosan and lysozyme (CMC/LYZ) nanogels with encapsulated amorphous calcium phosphate (ACP) based on the transformation of ACP to HAP. In this work, CMC/LYZ was used to stabilize ACP and form CMC/LYZ-ACP nanogels, and then the nanogel-encapsulated ACP was applied to exposed dentinal tubule surfaces. The morphology of the nanogels was examined by transmission electron microscopy (TEM). Distribution and quantity of elements in CMC/LYZ-ACP nanogels were determined by element mapping and energy dispersive X-Ray spectroscopy (EDX). Scanning electron microscopy (SEM) images, XRD measurements and nanoindentation were applied to check the efficacy of tubular occlusion. TEM revealed that CMC/LYZ-ACP nanogels were spherical dense gel particles with size approximately 50-500 nm. Element mapping and EDX indicated that C, N, O, Ca, P, and S in the microspheres are thoroughly represented. SEM images shows that the thickness of the coating layer was approximately 1-2 μm and the depth to which the mineralized substance enters the dentinal tubule was approximately 4-8 μm. XRD measurements and nanoindentation indicated that the occluding mineralized substance observed were similar to nature dentin. CMC can form spherical dense nanogels loaded with ACP under the participation of lysozyme. The CMC/LYZ-ACP nanogels could increase the dentinal tubule occluding effectiveness. These results indicated that finding and developing novel nanomaterials of CMC/LYZ-ACP would be an effective strategy for the treatment of dentin hypersensitivity.

Effect of physical interactions on structure of lysozyme in presence of three kinds of polysaccharides

In this work the influences of κ-carrageenan (CRG), konjac glucomannan (KGM) and inulin on lysozyme (Ly)'s structure, activity, and their complex phase behavior were investigated through spectroscopy and activity measurement in heated and unheated conditions. It was found that the impact on the structure and activity of Ly was determined by the interactions with polysaccharides. After heat treatment, KGM and CRG improved the stability of complex systems. However, inulin did not have significant impact. Heating process promoted to change the structure of Ly, and the intervention retard following the sequence of CRG > KGM > inulin. The worthwhile work indicated protein's structure and activity could be regulated by the interaction with polysaccharide, which might provide theoretical basis for food preservation and processing in different temperature treatments. Besides, the bidirectional effects of polysaccharide on protein would be beneficial to rational selection of functional properties of polysaccharide/protein systems.

A protein-dye hybrid system as a narrow range tunable intracellular pH sensor

Accurate monitoring of pH variations inside cells is important for the early diagnosis of diseases such as cancer. Even though a variety of different pH sensors are available, construction of a custom-made sensor array for measuring minute variations in a narrow biological pH window, using easily available constituents, is a challenge. Here we report two-component hybrid sensors derived from a protein and organic dye nanoparticles whose sensitivity range can be tuned by choosing different ratios of the components, to monitor the minute pH variations in a given system. The dye interacts noncovalently with the protein at lower pH and covalently at higher pH, triggering two distinguishable fluorescent signals at 700 and 480 nm, respectively. The pH sensitivity region of the probe can be tuned for every unit of the pH window resulting in custom-made pH sensors. These narrow range tunable pH sensors have been used to monitor pH variations in HeLa cells using the fluorescence imaging technique.

Adsorption of poly acrylic acid onto the surface of calcite: an experimental and simulation study

Macromolecular binding to minerals is of great importance in the formation of biofilms, and carboxylate functional groups have been found to play a pivotal role in the functioning of these macromolecules. Here we present both fluorescence time-resolved anisotropy measurements and simulation data on the conformational behaviour and binding of a poly acrylic acid polymer. In solution the polymer exhibits a pH dependent behaviour, with a coiled conformation at a low pH and extended conformation at higher pH values. The polymer is readily adsorbed on the surface of calcite, preferring to bind in an extended conformation, with the strength of the adsorption dependent on the pH and presence of counter ions. We discuss the reasons why the calculated adsorption free energy differs from that obtained from a Langmuir isotherm analysis, showing that they refer to different quantities. The enhanced binding of the extended conformations shows the importance of flexibility in the binding of macromolecules.

Self-assembled lysozyme/carboxymethylcellulose nanogels for delivery of methotrexate

Nanogels (NGs) were fabricated with lysozyme and carboxymethylcellulose via a green self-assembly method. The prepared NGs were characterized by dynamic light scattering (DLS), zeta potential, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Pyrene and isothiocyanate were introduced as fluorescent probes to research the hydrophobic area of the NGs and cells endocytosis, respectively. Methotrexate (MTX) was used to investigate the drug encapsulation property of the NGs. It turned out to be that the drug loaded NGs were regular spherical shape with a hydrodynamic diameter of about 123 nm. The drug loading efficiency was about 14.2%. The NGs can slowly release the drug and increase the bioavailability of the loaded drug. The NGs are promising carriers for the delivery of drugs and other bioactive molecules.

Coacervate-directed synthesis of CaCO3 microcarriers for pH-responsive delivery of biomolecules

pH-responsive, protein loaded calcium carbonate microcarriers are synthesized by the combination of complex coacervation and mineralization for drug delivery applications.