Quan Bai

Preparation of lysozyme molecularly imprinted polymers and purification of lysozyme from egg white.

Molecular imprinting as a promising and facile separation technique has received much attention because of its high selectivity for target molecules. In this study, lysozyme molecularly imprinted polymers (Lys-MIPs) were successfully prepared by the entrapment method with lysozyme as the template molecule, acrylamide as the functional monomer and N,N-methylenebisacrylamide as the cross-linker. The removal of the template lysozyme from the molecularly imprinted polymers was investigated in detail by two methods. The synthesized Lys-MIPs were characterized by scanning electron microscopy and Fourier transform-infrared, and the adsorption capacity, selectivity and reproducibility of the Lys-MIPs were also evaluated. The maximum adsorption capacity reached 94.8 mg/g, which is twice that of nonmolecularly imprinted polymers, and satisfactory selectivity and reproducibility were achieved. Using the Lys-MIP column, lysozyme could be separated completely from egg white, with purity close to 100% and mass recovery of 98.2%. This illustrated that the synthesized Lys-MIPs had high specific recognition and selectivity to the template lysozyme when they were applied to a mixture of protein standards and a real sample.

Preparation of core-shell structure Fe3 O4 @SiO2 superparamagnetic microspheres immoblized with iminodiacetic acid as immobilized metal ion affinity adsorbents for His-tag protein purification.

The core-shell structure Fe3 O4 /SiO2 magnetic microspheres were prepared by a sol-gel method, and immobiled with iminodiacetic acid (IDA) as metal ion affinity ligands for protein adsorption. The size, morphology, magnetic properties and surface modification of magnetic silica nanospheres were characterized by various modern analytical instruments. It was shown that the magnetic silica nanospheres exhibited superparamagnetism with saturation magnetization values of up to 58.1 emu/g. Three divalent metal ions, Cu(2+) , Ni(2+) and Zn(2+) , were chelated on the Fe3 O4 @SiO2 -IDA magnetic microspheres to adsorb lysozyme. The results indicated that Ni(2+) -chelating magnetic microspheres had the maximum adsorption capacity for lysozyme of 51.0 mg/g, adsorption equilibrium could be achieved within 60 min and the adsorbed protein could be easily eluted. Furthermore, the synthesized Fe3 O4 @SiO2 -IDA-Ni(2+) magnetic microspheres were successfully applied for selective enrichment lysozyme from egg white and His-tag recombinant Homer 1a from the inclusion extraction expressed in Escherichia coli. The result indicated that the magnetic microspheres showed unique characteristics of high selective separation behavior of protein mixture, low nonspecific adsorption, and easy handling. This demonstrates that the magnetic silica microspheres can be used efficiently in protein separation or purification and show great potential in the pretreatment of the biological sample.

Preparation of a weak anion exchange/hydrophobic interaction dual-function mixed-mode chromatography stationary phase for protein separation using click chemistry.

In this study, 3-diethylamino-1-propyne was covalently bonded to the azide-silica by a click reaction to obtain a novel dual-function mixed-mode chromatography stationary phase for protein separation with a ligand containing tertiary amine and two ethyl groups capable of electrostatic and hydrophobic interaction functionalities, which can display hydrophobic interaction chromatography character in a high-salt-concentration mobile phase and weak anion exchange character in a low-salt-concentration mobile phase employed for protein separation. As a result, it can be employed to separate proteins with weak anion exchange and hydrophobic interaction modes, respectively. The resolution and selectivity of the stationary phase were evaluated in both hydrophobic interaction and ion exchange modes with standard proteins, respectively, which can be comparable to that of conventional weak anion exchange and hydrophobic interaction chromatography columns. Therefore, the synthesized weak anion exchange/hydrophobic interaction dual-function mixed-mode chromatography column can be used to replace two corresponding conventional weak anion exchange and hydrophobic interaction chromatography columns to separate proteins. Based on this mixed-mode chromatography stationary phase, a new off-line two-dimensional liquid chromatography technology using only a single dual-function mixed-mode chromatography column was developed. Nine kinds of tested proteins can be separated completely using the developed method within 2.0 h.

Preparation and characterization of monodisperse large-porous silica microspheres as the matrix for protein separation

High performance liquid chromatography (HPLC) is a kind of efficient separation technology and has been used widely in many fields. Micro-sized porous silica microspheres as the most popular matrix have been used for fast separation and analysis in HPLC. In this paper, the monodisperse large-porous silica microspheres with controllable size and structure were successfully synthesized with polymer microspheres as the templates and characterized. First, the poly(glycidyl methacrylate-co-ethyleneglycol dimethacrylate) microspheres (PGMA-EDMA) were functionalized with tetraethylenepentamine (TEPA) to generate amino groups which act as a catalyst in hydrolysis of tetraethyl orthosilicate (TEOS) to form Si-containing low molecular weight species. Then the low molecular weight species diffused into the functionalized PGMA-EDMA microspheres by induction force of the amino groups to form polymer/silica hybrid microspheres. Finally, the organic polymer templates were removed by calcination, and the large-porous silica microspheres were obtained. The compositions, morphology, size distribution, specific surface area and pore size distribution of the porous silica microspheres were characterized by infrared analyzer, scanning-electron microscopy, dynamic laser scattering, the mercury intrusion method and thermal gravimetric analysis, respectively. The results show that the agglomeration of the hybrid microspheres can be overcome when the templates were functionalized with TEPA as amination reagent, and the yield of 95.7% of the monodisperse large-porous silica microspheres can be achieved with high concentration of polymer templates. The resulting large-porous silica microspheres were modified with octadecyltrichlorosilane (ODS) and the chromatographic evaluation was performed by separating the proteins and the digest of BSA. The baseline separation of seven kinds of protein standards was achieved, and the column delivered a better performance when separating BSA digests comparing with the commercial one currently available. The high column efficiency and good reproducibility present that the large-porous silica microspheres obtained can be used as a matrix for peptide and protein separation.

One-step refolding and purification of recombinant human tumor necrosis factor-α (rhTNF-α) using ion-exchange chromatography.

Protein refolding is a key step for the production of recombinant proteins, especially at large scales, and usually their yields are very low. Chromatographic-based protein refolding techniques have proven to be superior to conventional dilution refolding methods. High refolding yield can be achieved using these methods compared with dilution refolding of proteins. In this work, recombinant human tumor necrosis factor-α (rhTNF-α) from inclusion bodies expressed in Escherichia coli was renatured with simultaneous purification by ion exchange chromatography with a DEAE Sepharose FF column. Several chromatographic parameters influencing the refolding yield of the denatured/reduced rhTNF-α, such as the urea concentration, pH value and concentration ratio of glutathione/oxidized glutathione in the mobile phase, were investigated in detail. Under optimal conditions, rhTNF-α can be renatured and purified simultaneously within 30 min by one step. Specific bioactivity of 2.18 × 10(8) IU/mg, purity of 95.2% and mass recovery of 76.8% of refolded rhTNF-α were achieved. Compared with the usual dilution method, the ion exchange chromatography method developed here is simple and more effective for rhTNF-α refolding in terms of specific bioactivity and mass recovery.

Protein separation using a novel silica-based RPLC/IEC mixed-mode stationary phase modified with N-methylimidazolium ionic liquid

Ionic liquids (ILs) immobilized on silica as a novel high-performance liquid chromatography (HPLC) stationary phase have attracted considerable attentions. However, it has not been applied to protein separation. In this paper, N-methylimidazolium IL-modified silica-based stationary phase (SilprMim) was prepared and investigated as a novel multi-interaction stationary phase with positive charges for protein separation. The results indicate that all of the basic proteins tested cannot be adsorbed on this novel stationary phase, whereas all of the acidic proteins tested can be retained, and the baseline separation of eight kinds of acidic protein standards can be achieved when being performed under reversed phase/ion-exchange chromatography (RPLC/IEC) mode. Compared with commonly used commercial C4 column, the novel stationary phase can show good selectivity and resolution to acidic proteins. The effects of acetonitrile and salt concentration, pH as well as the ligand structure on protein separation were investigated in detail. In addition, the mix-mode retention mechanism of proteins on the SilprMim column was also discussed using stoichiometric displacement theory for retention in LC (SDT-R). The result shows that the protein retention can be controlled mainly by the electrostatic and hydrophobic interactions between the proteins and the stationary phase. As a result, with such characteristics of multi-interaction mechanism and multi-modal separation, not only the selectivity to the acidic proteins can be enhanced, but also a better resolution can be achieved. The result demonstrates that the SilprMim mixed-mode chromatography (MMC) column has a promising application in the separation and analysis of acidic proteins from the complex samples.

Fast separation and preparation of proteomics samples of human serum using high performance hydrophobic interaction chromatographic cake

A method for the fast separation of human serum and enrichment of low abundance proteins was developed using offline 2D liquid chromatography (2D-LC) consisted of chromatographic cake (10 mm x 20 mm i. d.) and reversed-phase liquid chromatography (RPLC). The protein after separation and enrichment was detected using matrix assisted laser desorption/ ionization time of flight mass spectrometry (MALDI-TOF MS). This method was validated by four standard proteins at very low concentration. It was found that the detection limits were 1 pmol/microL for the enriched cytochrome-c and myoglobin, and 0.1 pmol/microL for enriched lysozyme and insulin. This method has been applied to the proteomic research of human serum, and it was found that the signal intensity and the number of detected proteins/peptides in MALDI-TOF MS increased with the increase of the loading sample volume of the human serum on chromatographic cake. A total of 285 fractions (M(r) < 15 000) were found when 1.0 mL serum sample was loaded on the chromatographic cake. In addition, cytochrome-c in low abundance was also separated and enriched successfully when 1 microg cytochrome-c was added into 0.5 mL original serum. The results showed that 2D-LC consisting of the chromatographic cake and RPLC was successfully applied to not only the fast separation and preparation of human serum sample with large loading volume in one cycle of analysis, but also the efficient isolation and enrichment of the lower abundance proteins/peptides in human serum. Moreover, it successfully increased the detection efficiency of the low abundance proteins/peptides in human serum with MALDI-TOF MS.