Protein adsorption to poly(ethylenimine)-modified Sepharose FF: VI. Partial charge neutralization drastically increases uptake rate

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.

Biochemical engineering in China

Chinese biochemical engineering is committed to supporting the chemical and food industries, to advance science and technology frontiers, and to meet major demands of Chinese society and national economic development. This paper reviews the development of biochemical engineering, strategic deployment of these technologies by the government, industrial demand, research progress, and breakthroughs in key technologies in China. Furthermore, the outlook for future developments in biochemical engineering in China is also discussed.

Purification and characterization of a novel phloretin-2'-O-glycosyltransferase favoring phloridzin biosynthesis

Phloretin-2'-O-glycosyltransferase (P2'GT) catalyzes the last glycosylation step in the biosynthesis of phloridzin that contributes to the flavor, color and health benefits of apples and processed apple products. In this work, a novel P2'GT of Malus x domestica (MdP2'GT) with a specific activity of 46.82 μkat/Kg protein toward phloretin and uridine diphosphate glucose (UDPG) at an optimal temperature of 30 °C and pH 8.0 was purified from the engineered Pichia pastoris broth to homogeneity by anion exchange chromatography, His-Trap affinity chromatography and gel filtration. The purified MdP2'GT was low N-glycosylated and secreted as a stable dimer with a molecular mass of 70.7 kDa in its native form. Importantly, MdP2'GT also exhibited activity towards quercetin and adenosine diphosphate glucose (ADPG), kaempferol and UDPG, quercetin and UDP-galactose, isoliquiritigenin and UDPG, and luteolin and UDPG, producing only one isoquercitrin, astragalin, hyperoside, isoliquiritin, or cynaroside, respectively. This broad spectrum of activities make MdP2'GT a promising biocatalyst for the industrial preparation of the corresponding polyphenol glycosides, preferably for their subsequent isolation and purification. Besides, MdP2'GT displayed the lowest K_m and the highest k_cat/K_m for phloretin and UDPG compared to all previously reported P2'GTs, making MdP2'GT favor phloridzin synthesis the most.