High uptake rate and extremely salt-tolerant behavior of protein adsorption to 900 kDa poly(allylamine)-modified Sepharose FF

Sequential diethylaminoethyl dextran-grafting and diethylaminoethyl modification improve the adsorption performance of anion exchangers

Ion exchangers with high adsorption capacity, fast mass transfer, and high salt-tolerance synchronously are highly desired for high-performance protein purification. Here, we propose a sequential diethylaminoethyl dextran-grafting and diethylaminoethyl chloride modification strategy to achieve high-performance anion exchangers. The advantages of the double-modification strategy lie in: (1) the introduction of diethylaminoethyl in the second modification has no diffusion limitation due to the small molecular size, thus a high ionic capacity; (2) the grafting ligands not only provide three-dimensional adsorption space for high adsorption capacitybut alsofacilitate surface diffusion of protein by chain delivery. The maximum adsorption capacity of the obtained anion exchangers for bovine serum albumin reaches 333 mg/mL, the ratio of effective pore diffusivity (De) to free solution diffusivity (D0) reaches 0.69, and the adsorption amount reaches 97 mg/mL even in 100 mmol/L NaCl concentration,. All these results demonstrate the proposed sequential modification strategy are promising for the preparation of high-performance ion exchangers.

Multi-size optimization of macroporous cellulose beads as protein anion exchangers: Effects of macropore size, protein size, and ligand length

Multi-size optimization of ion exchangers based on protein characteristics and understanding of underlying mechanism is crucial to achieve maximum separation performance in terms of adsorption capacity and uptake kinetic. Herein, we characterize the effects of three different sizes, macropore size, protein size, and ligand length, on the protein adsorption capacity and uptake kinetic of macroporous cellulose beads, and provide insights into the underlying mechanism. In detail, (1) for smaller bovine serum albumin, macropore size has a negligible effect on the adsorption capacity, while for larger γ-globulin, larger macropores improve the adsorption capacity due to the high accessibility of binding sites; (2) there is a critical pore size (CPZ), at which the adsorption uptake kinetic is minimum. When pore sizes are higher than the CPZ, uptake kinetics are enhanced by pore diffusion. When pore sizes are lower than CPZ, uptake kinetics are enhanced by surface diffusion; (3) increasing ligand length improves the adsorption capacity by three-dimensionally extended polymer chains in pores and enhances uptake kinetic by improved surface diffusion. This study offers an integrated perspective to qualitatively assess the effects of multiple sizes, providing guidance for designing advanced ion exchangers for protein chromatography.

Recent advances in protein chromatography with polymer-grafted media

The strategy of using polymer-grafted media is effective to create protein chromatography of high capacity and uptake rate, giving rise to an excellent performance in high-throughput protein separation due to its high dynamic binding capacity. Taking the scientific development and technological innovation of protein chromatography as the objective, this review is devoted to an overview of polymer-grafted media reported in the last five years, including their fabrication routes, protein adsorption and chromatography, mechanisms behind the adsorption behaviors, limitations of polymer-grafted media and chromatographic operation strategies. Particular emphasis is placed on the elaboration and discussion on the behaviors of ion-exchange chromatography (IEC) with polymer-grafted media because IEC is the most suitable chromatographic mode for this kind of media. Recent advances in both the theoretical and experimental investigations on polymer-grafted media are discussed by focusing on their implications to the rational design of novel chromatographic media and mobile phase conditions for the development of high-performance protein chromatography. It is concluded that polymer-grafted media are suitable for development of IEC and mixed-mode chromatography with charged and low hydrophobic ligands, but not for hydrophobic interaction chromatography with high hydrophobic ligands and affinity chromatography with ligands that have single binding site on the protein.

Protein adsorption to poly(2-aminoethyl methacrylate)-grafted Sepharose gel: Effects of chain length and charge density

Grafting functional polymer chains onto porous resins has been found to drastically increase both adsorption capacity and uptake rate in protein chromatography. In this work, 2-aminoethyl methacrylate (AEM) was used for grafting onto Sepharose FF gel, and six anion-exchangers of different polyAEM (pAEM) chain lengths (ionic capacities, ICs), FF-pAEM, were obtained for protein adsorption and chromatography. It was found that protein adsorption capacity (q_m) increased with increasing pAEM chain length, but the uptake rate, represented by the ratio of effective pore diffusivity to the free solution diffusivity (D_e/D₀), showed an up-down trend, reaching a peak value (D_e/D₀=0.55) at an IC of 313 mmol/L. Partial charge neutralization of the AEM-grafted resin of the highest IC (513 mmol/L) by reaction with sodium acetate produced three charge-reduced resins, FF-pAEM513-R. With reducing the charge density, the adsorption capacity kept unchanged and then decreased, but the uptake rate monotonically increased, reaching a maximum (about 2-fold increase) at a residual IC of 263 mmol/L. It is notable that, at the same IC, the charge-reduced resin (FF-pAEM513-R) presented similar or even higher values of q_m and D_e/D₀ than its FF-pAEM counterpart. Particularly, at the same IC of 263 mmol/L, a ~50% enhancement of D_e/D₀ was observed. Both adsorption capacity and uptake rate in the charge-reduced resin with a residual IC of 339 mmo/L (FF-pAEM513-R339) decreased more sharply with increasing NaCl concentration by comparison with FF-pAEM513, indicating its increased salt-sensitivity than FF-pAEM513. That is, charge reduction on the AEM-grafted resin could accelerate protein uptake at 0 mmol/L NaCl but decrease salt tolerance. Column breakthrough experiments showed that FF-pAEM513-R339 was favorable for high flow rate protein chromatography at low NaCl concentration (0 mmol/L), whereas FF-pAEM513 was a good choice in a wide range of salt concentrations at low flow rate. This research proved the excellent protein chromatography performance of the AEM-based anion-exchangers.