Affinity Chromatography

A bio-coupling approach using a dextran-binding domain to immobilize an engineered streptavidin to Sephadex for easy preparation of affinity matrix

An engineered streptavidin, SAVSBPM18 with reversible biotin binding capability, has been successfully applied to purify biotinylated and streptavidin-binding peptide (SBP) tagged proteins. To simplify the preparation for the SAVSBPM18 affinity matrix without chemical conjugation, two bio-coupling approaches were developed based on a 14-kDa dextran-binding domain (DBD) from a Leuconostoc mesenteroides dextransucrase. The first approach offers simplicity for bio-coupling by creating a direct fusion, SAVSBPM18-Linker-DBD. Purification of the fusion from crude extract and its immobilization to Sephadex can be consolidated in one-step. The second approach aims at flexibility. A SnoopCatcher (SC) was fused to DBD to create SC-Linker-DBD. This fusion can covalently capture any recombinant proteins tagged with a SnoopTag (ST) including SAVSBPM18-Linker-ST via the formation of an isopeptide bond at the interface through the SnoopCatcher-SnoopTag interaction. Although monomeric DBD binds to dextran with nanomolar affinity, DBD tetramerized via streptavidin (SAVSBPM18-Linker-ST·SC-Linker-DBD) showed an even tighter binding to Sephadex. The majority of the fluorescently labelled DBD tetramers were retained on the Sephadex surface even after four months. Affinity columns generated using either approach effectively purified both SBP-tagged and biotinylated proteins. These columns are reusable and functional even after a year of frequent use.

Facile one-pot synthesis of a aptamer-based organic-silica hybrid monolithic capillary column by "thiol-ene" click chemistry for detection of enantiomers of chemotherapeutic anthracyclines

In the current study, we developed a facile strategy for the one-pot synthesis of an aptamer-based organic-silica hybrid monolithic capillary column. A 5'-SH-modified aptamer, specifically targeting doxorubicin, was covalently modified in the hybrid silica monolithic column by a sol-gel method combined with "thiol-ene" click reaction. The prepared monolithic column had good stability and permeability, large specific surface, and showed excellent selectivity towards chemotherapeutic anthracyclines of doxorubicin and epirubicin. In addition, the enantiomers of doxorubicin and epirubicin can be easily separated by aptamer-based affinity monolithic capillary liquid chromatography. Furthermore, doxorubicin and epirubicin spiked in serum and urine were also successfully determined, which suggested that the complex biological matrix had a negligible effect on the detection of doxorubicin and epirubicin. Finally, we quantified the concentration of epirubicin in the serum of breast cancer patients treated with epirubicin by intravenous injection. The developed analytical method is cost-effective and rapid, and biological samples can be directly analyzed without any tedious sample pretreatment, which is extremely useful for monitoring medicines in serum and urine for pharmacokinetic studies.

Membrane adsorbers comprising grafted glycopolymers for targeted lectin binding

This work details the design and testing of affinity membrane adsorbers for lectin purifications that incorporate glucose-containing glycopolymers. It is the selective interaction between the sugar residues of the glycopolymer and the complementary carbohydrate-binding domain of the lectin that provides the basis for the isolation and purification of lectins from complex biological media. The design approach used in these studies was to graft glycopolymer 'tentacles' from macroporous regenerated cellulose membranes by atom transfer radical polymerization. As shown in earlier studies, this design approach can be used to prepare high-productivity membrane adsorbers. The model lectin, concanavalin A (conA), was used to evaluate membrane performance in bind-and-elute purification, using a low molecular weight sugar for elution. The membrane capacity for binding conA was measured at equilibrium and under dynamic conditions using flow rates of 0.1 and 1.0 mL/min. The first Damkohler number was estimated to relate the adsorption rate to the convective mass transport rate through the membrane bed. It was used to assess whether adsorption kinetics or mass transport contributed the primary limitation to conA binding. Analyses indicate that this system is not limited by the accessibility of the binding sites, but by the inherent rate of adsorption of conA onto the glycopolymer.