Microcalorimetric study of the adsorption of PEGylated lysozyme and PEG on a mildly hydrophobic resin: influence of ammonium sulfate

Adsorption of conjugates of lysozyme and fluorescein isothiocyanate in hydrophobic interaction chromatography

Bioconjugates, such as antibody-drug conjugates or fluorescent-labeled proteins, are highly interesting for various applications in medicine and biology. In their production, not only the synthesis is challenging but also the downstream processing, for which hydrophobic interaction chromatography (HIC) is often used. However, in-depth studies of the adsorption of bioconjugates in HIC are still rare. Therefore, in the present work, three different conjugates of lysozyme and fluorescein isothiocyanate (FITC) were synthesized and isolated, and their adsorption on the hydrophobic resin Toyopearl PPG-600 M was systematically studied in batch experiments. The influence of sodium chloride and ammonium sulfate with ionic strengths up to 2000 mM on the adsorption isotherms was investigated at pH 7.0 and 25 °C, and the results were compared to those for pure lysozyme. The conjugation leads to an increase of the adsorption in all studied cases. All studied conjugates contain only a single FITC and differ only in the position of the conjugation on the lysozyme. Despite this, strong differences in the adsorption behavior were observed. Moreover, a mathematical model was developed, which enables the prediction of the adsorption isotherms in the studied systems for varying ionic strengths.

Influence of pH value and salts on the adsorption of lysozyme in mixed-mode chromatography

Mixed-mode chromatography (MMC) is an interesting technique for challenging protein separation processes which typically combines adsorption mechanisms of ion exchange (IEC) and hydrophobic interaction chromatography (HIC). Adsorption equilibria in MMC depend on multiple parameters but systematic studies on their influence are scarce. In the present work, the influence of the pH value and ionic strengths up to 3000 mM of four technically relevant salts (sodium chloride, sodium sulfate, ammonium chloride, and ammonium sulfate) on the lysozyme adsorption on the mixed-mode resin Toyopearl MX-Trp-650M was studied systematically at 25℃. Equilibrium adsorption isotherms at pH 5.0 and 6.0 were measured and compared to experimental data at pH 7.0 from previous work. For all pH values, an exponential decay of the lysozyme loading with increasing ionic strength was observed. The influence of the pH value was found to depend significantly on the ionic strength with the strongest influence at low ionic strengths where increasing pH values lead to decreasing lysozyme loadings. Furthermore, a mathematical model that describes the influence of salts and the pH value on the adsorption of lysozyme in MMC is presented. The model enables predicting adsorption isotherms of lysozyme on Toyopearl MX-Trp-650M for a broad range of technically relevant conditions.

Correlation between protein desorption behavior and its adsorption enthalpy change in polymer grafted anion exchange chromatography

Thermodynamic studies on protein adsorption onto chromatographic surfaces mainly focus on the molecular level interaction between proteins and ligands. Yet, not much attention is given to the study of polymer grafted ligand architecture effect on thermodynamic parameters, nor to the relation between chromatographic parameters and the directly obtained thermodynamic parameters. These relations are needed in order to confer meaning and to ease future data interpretation of thermodynamic studies of protein adsorption. In this study, the adsorption of bovine serum albumin monomer (BSA_m) onto chromatographic surfaces with grafted ligands was studied from a thermodynamic point of view together with chromatographic data. Isothermal titration calorimetry (ITC) results showed that BSA_m adsorption is exothermic (ΔH¯^ads < 0) when adsorbs onto Toyopearl GigaCapQ 650 M, Toyopearl Q600AR, and Q Sepharose XL, but endothermic (ΔH¯^ads > 0) when adsorbs onto Toyopearl SuperQ and a conventional resin (Q Sepharose Fast Flow), showing clear differences in the driving forces of adsorption caused by different ligand architectures. In addition, we found a new relation between the salt required for protein elution and the change in adsorption enthalpy (ΔH¯^ads) directly measured with ITC, intrinsically connecting both adsorption and desorption mechanisms.

Influence of Salts on the Adsorption of Lysozyme on a Mixed-Mode Resin

Mixed-mode chromatography (MMC), which combines features of ion exchange chromatography (IEC) and hydrophobic interaction chromatography (HIC), is an interesting method for protein separation and purification. The design of MMC processes is challenging as adsorption equilibria are influenced by many parameters, including ionic strength and the presence of different salts in solution. Systematic studies on the influence of those parameters in MMC are rare. Therefore, in the present work, the influence of four salts, namely, sodium chloride, sodium sulfate, ammonium chloride, and ammonium sulfate, on the adsorption of lysozyme on the mixed-mode resin Toyopearl MX-Trp-650M at pH 7.0 and 25°C was studied systematically in equilibrium adsorption experiments for ionic strengths between 0 mM and 3000 mM. For all salts, a noticeable adsorption strength was observed over the entire range of studied ionic strengths. An exponential decay of the loading of the resin with increasing ionic strength was found until approx. 1000 mM. For higher ionic strengths, the loading was found to be practically independent of the ionic strength. At constant ionic strength, the highest lysozyme loadings were observed for ammonium sulfate, the lowest for sodium chloride. A mathematical model was developed that correctly describes the influence of the ionic strength as well as the influence of the studied salts. The model is the first that enables the prediction of adsorption isotherms of proteins on mixed-mode resins in a wide range of technically interesting conditions, accounting for the influence of the ionic strength and four salts of practical relevance.

Microcalorimetric Analysis of the Adsorption of Lysozyme and Cytochrome c onto Cation-Exchange Chromatography Resins: Influence of Temperature on Retention

We studied the adsorption mechanism of two basic proteins, equine cytochrome c (Cyt) and chicken egg-white lysozyme (Lys), adsorbing onto negatively charged chromatography surfaces. In liquid chromatography, the retention volume of Lys was larger than that of Cyt on negatively charged ion-exchange resins. When the temperature increased, the retention volume of Cyt increased, whereas that of Lys clearly decreased. Both Lys and Cyt share similar physical characteristics, so the opposite behavior with increasing temperatures was surprising, indicating a more complex mechanism of adsorption may be involved. We analyzed the adsorption of these proteins by using isothermal titration calorimetry (ITC). The change in adsorption enthalpy determined by ITC allowed the understanding of the reason for and underlying driving forces of protein adsorption that resulted in this opposite behavior. Large exothermic enthalpies of adsorption were observed for Lys (-43.95 kJ/mol), and Lys adsorption was found to be enthalpically driven. On the other hand, endothermic enthalpies were dominant for Cyt adsorption (32.41 kJ/mol), which was entropically driven. These results indicate that dehydration and release of counterions play a more important role in Cyt adsorption and ionic interaction and hydrogen bridges are more significant in Lys adsorption. Understanding of the adsorption mechanism of proteins onto chromatography resins is essential for modeling and developing new, efficient chromatographic processes.

Influence of pH and Salts on Partial Molar Volume of Lysozyme and Bovine Serum Albumin in Aqueous Solutions

The partial molar volume of lysozyme and bovine serum albumin in aqueous solutions at different pH values and in aqueous solutions containing sodium chloride, ammonium chloride, sodium sulfate, or ammonium sulfate at different concentrations at pH 7.0 was investigated experimentally at 298.15 K and 1 bar. It was found that the influence of the pH value and the salts on the partial molar volume of the proteins is small, but trends were measurable. Furthermore, the partial molar volume of lysozyme in pure water at different pH values and in aqueous solutions with different sodium chloride concentrations at pH 7.0 was predicted by molecular simulations. The predictions are in good agreement with the experimental data.

Hydrophobic interaction chromatography of proteins: Studies of unfolding upon adsorption by isothermal titration calorimetry

Heat of adsorption is an excellent measure for adsorption strength and, therefore, very useful to study the influence of salt and temperature in hydrophobic interaction chromatography. The adsorption of bovine serum albumin and β-lactoglobulin to Toyopearl Butyl-650 M was studied with isothermal titration calorimetry to follow the unfolding of proteins on hydrophobic surfaces. Isothermal titration calorimetry is established as an experimental method to track conformational changes of proteins on stationary phases. Experiments were carried out at two different salt concentrations and five different temperatures. Protein unfolding, as indicated by large changes of molar enthalpy of adsorption Δh_ads , was observed to be dependent on temperature and salt concentration. Δh_ads were significantly higher for bovine serum albumin and ranged from 578 (288 K) to 811 (308 K) kJ/mol for 1.2 mol/kg ammonium sulfate. Δh_ads for β-lactoglobulin ranged from 129 kJ/mol (288 K) to 186 kJ/mol (308 K). For both proteins, Δh_ads increased with increasing temperature. The influence of salt concentration on Δh_ads was also more pronounced for bovine serum albumin than for β-lactoglobulin. The comparison of retention analysis evaluated by the van't Hoff algorithm shows that beyond adsorption other processes occur simultaneously. Further interpretation such as unfolding upon adsorption needs other in situ techniques.

Photoactive fluoropolymer surfaces that release sensitizer drug molecules

We describe a physical-organic study of two fluoropolymers bearing a photoreleasable PEGylated photosensitizer that generates (1)O2((1)Δg) [chlorin e6 methoxy tri(ethylene glycol) triester]. The surfaces are Teflon/poly(vinyl alcohol) (PVA) nanocomposite and fluorinated silica. The relative efficiency of these surfaces to photorelease the PEGylated sensitizer [shown previously to be phototoxic to ovarian cancer cells (Kimani, S. et al. J. Org. Chem 2012, 77, 10638)] was slightly higher for the nanocomposite. In the presence of red light and O2, (1)O2 is formed, which cleaves an ethene linkage to liberate the sensitizer in 68-92% yield. The fluoropolymers were designed to deal with multiple problems. Namely, their success relied not only on high O2 solubility and drug repellency but also on the C-F bonds, which physically quench little (1)O2, for singlet oxygen's productive use away from the surface. The results obtained here indicate that Teflon-like surfaces have potential uses in delivering sensitizer and singlet oxygen for applications in tissue repair and photodynamic therapy (PDT).

Kosmotrope-like hydration behavior of polyethylene glycol from microcalorimetry and binding isotherm measurements

Polyethylene glycol (PEG) at various molecular weights (MWs) has been regarded as a wonder molecule in biomedical applications. For instance, PEG serves as a unique moiety for pegylation of "biobetter" drug development, PEG provides controlled-release and preserved activity of biologics, and PEG modified surface works as an antibiofouling surface. The primary characteristics of PEG molecules used in relevant applications have been attributed mainly to the hydration behavior in aqueous solutions. However, the effects on the solvation of solutes in solution caused by presenting PEG molecules as a cosolvent, as well as the thermodynamics aspect of the hydration behavior of PEG in solution, have not been well documented. The solvation behavior of solutes, such as protein, with PEG as a cosolvent, indicates the success of PEG applications, such as biofouling and controlled release. In this investigation, we examined the effects of a buffer solution containing PEG molecules on the solution behavior of solute and the interactions between solid surfaces with solutes. We adapted the study by selecting a lysozyme as a solute in a buffer solution with either ammonium sulfate (kosmotrope) or sodium chloride (chaotrope) and anionic resin (SP-Sepharose) as solid surfaces. The experiments primarily involved binding equilibrium measurements and thermodynamics analysis. The results revealed that, in both saline buffers, adding PEG increases the binding affinity between the lysozyme and the resin, similar to kosmotropic salt in the examined salt concentrations. The thermodynamics analyses involving microcalorimetric measurements show that the bindings are mainly driven by enthalpy, indicating that electrostatic interaction was the primary binding force under these experimental conditions. The variations of the enthalpy and entropy of the binding thermodynamics when adding PEG to different salt types in the buffer solution showed opposite behavior, and the results support the concept of kosmotrope-like behavior of PEG. The equilibrium and thermodynamics data demonstrate that PEG has a kosmotrope-like hydration behavior, and the extent of kosmotrope-like behavior depends on the molecular weight of PEG with the outcomes of various molecular weights of PEG being added to the binding solution. The results of this study provide essential knowledge for PEG as an additive (or cosolvent) in various research applications.