Xavier Santarelli

Antibody capture by mixed-mode chromatography: a comprehensive study from determination of optimal purification conditions to identification of contaminating host cell proteins.

We evaluated mixed mode chromatography for the capture of recombinant antibodies from CHO cell culture supernatants. We studied PPA HyperCel, HEA HyperCel, MEP HyperCel and Capto adhere resins, which all contain hydrophobic and cationic groups. A microplate approach combined with DoE modeling allowed the exploration of the complex behaviors of these mixed mode resins. Optimal conditions for antibody purification and host cell proteins (HCPs) elimination were determined and then directly up-scaled to laboratory columns. Then we used mass spectrometry to identify the major HCPs potentially coeluted with the antibody. Differences between the four resins in terms of amount, complexity and identity of the HCPs present in the elution fractions were investigated.

Cation exchange versus multimodal cation exchange resins for antibody capture from CHO supernatants: Identification of contaminating Host Cell Proteins by mass spectrometry

We compared classical and multimodal cation exchange resins for the capture of recombinant antibodies from Chinese hamster ovary (CHO) cell culture supernatant. Both Capto S and Capto MMC resins present anionic groups while the multimodal Capto MMC also features a hydrophobic moiety. First we screened optimal binding and elution conditions in microplates with a pure antibody. We validated the results on the lab-scale with columns with a pure antibody and a CHO cell culture supernatant. Both resins achieved good yield and purity for the capture step of an antibody. However, the multimodal resin appeared more efficient and selective. Then we identified proteins in the antibody fraction by mass spectrometry in order to highlight the behavior of host cell proteins (HCPs).

Structure-activity relationship of human liver-expressed antimicrobial peptide 2.

Liver-expressed antimicrobial peptide 2 (LEAP-2) is a 40-residue cationic peptide originally purified from human blood ultrafiltrate. The native peptide contains two disulfide bonds and is unique regarding its primary structure. Its biological role is not known but a previous study showed that chemically synthesized LEAP-2 exhibited in vitro antimicrobial activities against several Gram-positive bacteria. In order to determine its antimicrobial mode of action, we expressed human recombinant LEAP-2 in Escherichia coli. Circular dichroism spectroscopy and nuclear magnetic resonance analyses showed that the structure of the recombinant peptide was identical to that of the chemically synthesized and oxidized LEAP-2, with two disulfide bonds between Cys residues in relative 1-3 and 2-4 positions. Minimal inhibitory concentration (MIC) of the recombinant human LEAP-2 was determined by a conventional broth dilution assay. It was found to be bactericidal against Bacillus megaterium at a 200microM concentration. Interestingly, the linear LEAP-2 had a greater antimicrobial activity with a MIC value of 12.5microM, which was comparable to that of magainin2. SYTOX Green uptake was used to assess bacterial membrane integrity. Linear LEAP-2 and magainin2 permeabilized B. megaterium membranes with the same efficiency, whereas oxidized LEAP-2 did not induce stain uptake. Binding of the peptides to plasmid DNA was evaluated by gel retardation assays. The DNA-binding efficacy of linear LEAP-2 was three times higher than that of the peptide-containing disulfide bridges. Altogether, these results show that the secondary structure of human LEAP-2 has a profound impact on its antibacterial activity.

Comparative study of strong anion exchangers: Structure-related chromatographic performances ☆

Chromatographic performances are highly influenced by operational parameters. New ion exchangers have tailored matrices providing low backpressure and allowing high flow velocity. By systematic frontal analysis and selectivity determination at different flow rates, we suggested an independent evaluation of major anion exchangers to facilitate media selection, and investigated the relationship between (i) surface modification and (ii) chromatographic performances. Structure-extended resins showed higher binding capacities compared to resins with conventional ligands directly attached to the matrix. Moreover, they maintained mainly high capacities even with extremely high flow velocities. Ligand accessibility was therefore largely enhanced, allowing proteins to interact and bind under harsh conditions. High throughput resins can be used for purification of high volume and high concentration feedstock in limited time. This results in higher productivity and could contribute to cost reduction.

A comprehensive evaluation of mixed mode interactions of HEA and PPA HyperCel™ chromatographic media.

Mixed mode or multimodal chromatography has been developed for rational use of multiple interactions in a controlled manner, in contrast to non-specific interactions. Indeed, as the term mixed mode suggests, these resins allow different types of interactions within a single chromatographic medium. In this paper, HEA HyperCel™, PPA HyperCel™ mixed-mode chromatographic media have been studied. These mixed-mode sorbents typically involve hydrophobic pseudo-affinity interactions for binding and essentially ionic interactions (charge repulsion) for elution. We identified and characterized these different interactions in chromatographic experiments by exploiting specific properties of proteins using protein standards and complex mixtures. We highlighted the major intervention of at least two types of interactions in these media: hydrophobic and electrostatic interactions. We observed the behaviour of these resins at different pH, ionic strength, with different salts and buffers types and in the presence of different organic compounds.

Rapid screening of purification strategies for the capture of a human recombinant F(ab )2 expressed in baculovirus-infected cells using a micro-plate approach and SELDI-MS

The development of a capture step of a human recombinant F(ab)(2) produced and expressed in baculovirus-infected cells was investigated by screening three mixed-mode chromatography sorbents (HEA HyperCel, PPA HyperCel and MEP HyperCel) and two ion exchangers (Q Ceramic HyperD F, S Ceramic HyperD F) sorbents using a 96-well plate format and SELDI-MS. HEA HyperCel gave the best separation performance therefore the conditions tested in micro-plate were transferred to laboratory scale chromatographic experiments, confirming that the recombinant F(ab)(2) was effectively captured on the mixed-mode sorbent without any pre-treatment of the crude extract with a 82% recovery and a 39-fold purification.

A study on the nature of interactions of mixed-mode ligands HEA and PPA HyperCel using phenylglyoxal modified lysozyme.

Mixed mode chromatography, or multimodal chromatography, involves the exploitation of combinations of several interactions in a controlled manner, to facilitate the rapid capture of proteins. Mixed-mode ligands like HEA and PPA HyperCel™ facilitate different kinds of interactions (hydrophobic, ionic, etc.) under different conditions. In order to better characterize the nature of this multi-modal interaction, we sought to study a protein, lysozyme, which is normally not retained by these mixed mode resins under normal binding conditions. Lysozyme was modified specifically at Arginine residues by the action of phenylglyoxal, and was extensively studied in this work to better characterize the mixed-mode interactions of HEA HyperCel™ and PPA HyperCel™ chromatographic supports. We show here that the adsorption behaviour of lysozyme on HEA and PPA HyperCel™ mixed mode sorbents varies depending on the degree of charge modification at the surface of the protein. Experiments using conventional cation exchange and hydrophobic interaction chromatography confirm that both charge and hydrophobicity modification occurs at the surface of the protein after lysozyme reaction with phenylglyoxal. The results emanating from this work using HEA and PPA HyperCel sorbents strongly suggest that mixed mode chromatography can efficiently separate closely related proteins of only minor surface charge and/or hydrophobicity differences.

Evidence for specific interaction between the RhoGAP domain from the yeast Rgd1 protein and phosphoinositides

The Rho GTPase activating protein Rgd1 increases the GTPase activity of Rho3p and Rho4p, which are involved in bud growth and cytokinesis, respectively, in the budding yeast Saccharomyces cerevisiae. Rgd1p is a member of the F-BAR family conserved in eukaryotes; indeed, in addition to the C-terminal RhoGAP domain Rgd1p possesses an F-BAR domain at its N-terminus. Phosphoinositides discriminate between the GTPase activities of Rho3p and Rho4p through Rgd1p and specifically stimulate the RhoGAP activity of Rgd1p on Rho4p. Determining specific interactions and resolving the structure of Rgd1p should provide insight into the functioning of this family of protein. We report the preparation of highly pure and functional RhoGAP domain of Rgd1 RhoGAP domain using a high yield expression procedure. By gel filtration and circular dichroïsm we provide the first evidences for a specific interaction between a RhoGAP domain (the RhoGAP domain of Rgd1p) and phosphoinositides.