The potential to combine aqueous two-phase extraction (ATPE) with magnetic separation was here investigated with the aim of developing a selective non-chromatographic method for the purification of antibodies from cell culture supernatants. Aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) and dextran were supplemented with several surface modified magnetic particles (MPs) at distinct salt concentrations. The partition of pure human IgG in the upper and lower phases as well as the amount adsorbed at the MPs surface was investigated, indicating that MPs coated with dextran and gum Arabic established the lowest amount of non-specific interactions. The binding capacity of gum arabic coated particles modified with aminophenyl boronic acid (GA-APBA-MP) was were found to be excellent in combination with the ATPS system, yielding high yields of antibody recovery (92%) and purity (98%) from cell culture supernatants. The presence of MPs in the ATPS was found to speed up phase separation (from 40 to 25 min), to consume a lower amount of MPs (half of the amount needed in magnetic fishing) and to increase the yield and purity of a mAb purified from a cell culture supernatant, when compared with ATPE or magnetic fishing processes alone.

FucoPol, a fucose-containing extracellular polysaccharide (EPS) produced by bacterium Enterobacter A47 using glycerol as the carbon source, was employed as a coating material for magnetic particles (MPs), which were subsequently functionalized with an artificial ligand for the capture of antibodies. The performance of the modified MPs (MP–EPS-22/8) for antibody purification was investigated using direct magnetic separation alone or combined with an aqueous two-phase system (ATPS) composed of polyethylene glycol (PEG) and dextran. In direct magnetic capturing, and using pure protein solutions of human immunoglobulin G (hIgG) and bovine serum albumin (BSA), MP–EPS-22/8 bound 120 mg hIgG g−1 MPs, whereas with BSA only 10 ± 2 mg BSA g−1 MPs was achieved. The hybrid process combining both the ATPS and magnetic capturing leads to a good performance for partitioning of hIgG in the desired phase as well as recovery by the magnetic separator. The MPs were able to bind 145 mg of hIgG g−1 of particles which is quite high when compared with direct magnetic separation. The theoretical maximum capacity was calculated to be 410 ± 15 mg hIgG adsorbed g−1 MPs with a binding affinity constant of 4.3 × 104 M−1. In multiple extraction steps, the MPs bound 92% of loaded hIgG with a final purity level of 98.5%. The MPs could easily be regenerated, recycled and re-used for five cycles with only minor loss of capacity. FucoPol coating allowed both electrostatic and hydrophobic interactions with the antibody contributing to enhance the specificity for the targeted products.

Aminophenyl boronic acids can form reversible covalent ester interactions with cis-diol-containing molecules, serving as a selective tool for binding glycoproteins as antibody molecules that possess oligosaccharides in both the Fv and Fc regions. In this study, amino phenyl boronic acid (APBA) magnetic particles (MPs) were applied for the magnetic separation of antibody molecules. Iron oxide MPs were firstly coated with dextran to avoid non-specific binding and then with 3-glycidyloxypropyl trimethoxysilane to allow further covalent coupling of APBA (APBA_MP). When contacted with pure protein solutions of human IgG (hIgG) and bovine serum albumin (BSA), APBA_MP bound 170 ± 10 mg hIgG g−1 MP and eluted 160 ± 5 mg hIgG g−1 MP, while binding only 15 ± 5 mg BSA g−1 MP. The affinity constant for the interaction between hIgG and APBA_MP was estimated as 4.9 × 105 M−1 (Ka) with a theoretical maximum capacity of 492 mg hIgG adsorbed g−1 MP (Qmax), whereas control particles bound a negligible amount of hIgG and presented an estimated theoretical maximum capacity of 3.1 mg hIgG adsorbed g−1 MP (Qmax). APBA_MPs were also tested for antibody purification directly from CHO cell supernatants. The particles were able to bind 98% of IgG loaded and to recover 95% of pure IgG (purity greater than 98%) at extremely mild conditions.

The WW domain derived from human Yes-associated protein (hYAP65_WW) recognizes proline-rich peptides. The structural and chemical robustness of WW domains makes them appealing candidates to target and capture these peptides in affinity purification processes. In this work{,} the chemical synthesis of the hYAP65_WW domain containing a terminal cysteine for oriented coupling onto the chromatographic matrix was successfully achieved by a fragment solution condensation reaction and by incorporation of pseudoproline dipeptide units. Both strategies yielded a hYAP65_WW protein with the characteristic WW domain folding. The purified hYAP65_WW domain was immobilized in a chromatographic matrix and tested for binding to a proline-rich peptide. The adsorbent bound 92 ng of peptide per mg of support and the elution was particularly efficient when employing a low pH or an increase in salt concentration. This work sets the ground for the application of WW domains as affinity reagents towards the capture and elution of peptides and proteins rich in proline sequences.

Iron oxide magnetic nanoparticles {(MNPs)} alone are suitable for a broad spectrum of applications, but the low stability and heterogeneous size distribution in aqueous medium represent major setbacks. These setbacks can however be reduced or diminished through the coating of {MNPs} with various polymers, especially biopolymers such as polysaccharides. Polysaccharides are biocompatible, non-toxic and renewable; in addition, they possess chemical groups that permit further functionalization of the {MNPs.} Multifunctional entities can be created through decoration with specific molecules e.g. proteins, peptides, drugs, antibodies, biomimetic ligands, transfection agents, cells, and other ligands. This development opens a whole range of applications for iron oxide nanoparticles. In this review the properties of magnetic structures composed of {MNPs} and several polysaccharides {(Agarose}, Alginate, Carrageenan, Chitosan, Dextran, Heparin, Gum Arabic, Pullulan and Starch) will be discussed, in view of their recent and future biomedical and biotechnological applications.

The human Pin1 WW domain (hPin1_WW) is a 38 residue protein which specifically recognizes ligands rich in proline and phosphorylated in Ser and Thr residues. This work presents a protocol for the improved chemical synthesis and modification of this protein through automated microwave assisted synthesis combined with the incorporation of pseudoproline units in the protein sequence. After purification{,} the protein was characterized by Mass Spectrometry and Circular Dichroism spectroscopy with results comparable to the same WW domain chemically synthesized by other strategies or biologically expressed. The protein was further immobilized on a matrix and tested for the selective binding and mild elution of phosphorylated sequences at Ser{,} Thr and Tyr residues. These results suggest that hPin1_WW is a useful protein scaffold for the purification of phosphorylated species in pTyr and pSer{,} which can be easily produced and modified by chemical methods.

Affinity purification is one of the most powerful separation techniques extensively employed both at laboratory and production scales. While antibodies still represent the gold standard affinity reagents, others derived from non-immunoglobulin scaffolds emerged as interesting alternatives in particular for affinity purification. The lower costs of production, fast ligand development and high robustness are appealing advantages of non-immunoglobulin scaffolds. These have successfully been used in the affinity purification of relevant targets as antibodies, human serum albumin, transferrin and other biomarkers, as reviewed in this work. Furthermore, a critical assessment on the strengths, weaknesses, opportunities and threats related with the implementation of non-immunoglobulin scaffolds as ligands in affinity purification are discussed. This article is protected by copyright. All rights reserved.