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Barbosa, AJM, Roque ACA.  2019.  Free Marine natural products databases for biotechnology and bioengineering. Biotechnology Journal. -(-):-. AbstractWebsite

Marine organisms and microorganisms are a source of natural compounds with unique chemical features. These chemical properties are useful for the discovery of new functions and applications of Marine Natural Products (MNP). To extensively exploit the potential implementations of MNPs, they are gathered in chemical databases consenting their study and screening for applications of biotechnological interest. However, classification of MNPs is currently poor in generic chemical databases. The present availability of free‐access focused MNPs databases is scarce and the molecular diversity of these databases is still very low when compared to paid‐access ones. In this review paper, the current scenario of free‐access MNP databases is presented as well as the hindrances involved in their development, mainly compound dereplication. Examples and opportunities on using freely accessible MNP databases in several important areas of biotechnology are also assessed. The scope of this paper is as well to notify the latent potential of these information sources for the discovery and development of new MNPs in biotechnology, and push future efforts to develop a public domain MNP database freely available for the scientific community.

Barbosa, AJM, Oliveira AR, Roque ACA.  2018.  Protein- and Peptide-Based Biosensors in Artificial Olfaction. Trends in Biotechnology. 36(12):1244-1258. AbstractPDFWebsite

Animals’ olfactory systems rely on proteins, olfactory receptors (ORs) and
odorant-binding proteins (OBPs), as their native sensing units to detect odours.
Recent advances demonstrate that these proteins can also be employed as
molecular recognition units in gas-phase biosensors. In addition, the interactions
between odorant molecules and ORs or OBPs are a source of inspiration
for designing peptides with tunable odorant selectivity. We review recent
progress in gas biosensors employing biological units (ORs, OBPs, and peptides)
in light of future developments in artificial olfaction, emphasizing examples
where biological components have been employed to detect gas-phase
analytes.

Barroso, T, Casimiro T, Ferraria A, Mattioli F, Aguiar-Ricardo A, Roque ACA.  2014.  Hybrid monoliths for magnetically-driven protein separations. Adv. Funct. Mater.. 24(28):4528–4541. AbstractWebsite

Monoliths represent powerful platforms for isolation of large molecules with high added value. This work presents a hybrid approach for antibody (Ab) capture and release. Using mostly natural polymers and clean processes, it is possible to create macroporous monoliths with well-defined porous networks, tuneable mechanical properties, and easy functionalization with a biomimetic ligand specific for Ab. Magnetic nanoparticles (MNPs) are embedded on the monolith network to confer a controlled magnetic response that facilitates and accelerates Ab recovery in the elution step. The hybrid monolithic systems prepared with agarose or chitosan/poly(vinyl alcohol) (PVA) blends exhibit promising binding capacities of Abs directly from cell-culture extracts (120 ± 10 mg Ab g−1 support) and controlled Ab magnetically-assisted elution yielding 95 ± 2% recovery. Moreover, a selective capture of mAbs directly from cell culture extracts is achieved yielding a final mAb preparation with 96% of purity.

Barroso, T, Hussain A, Roque ACA, Aguiar‐Ricardo A.  2013.  Functional monolithic platforms: Chromatographic tools for antibody purification. Biotechnology journal. 8(6):671–681. AbstractWebsite

Polymer monoliths are an efficient platform for antibody purification. The use of monoclonal antibodies (mAbs) and engineered antibody structures as therapeutics has increased exponentially over the past few decades. Several approaches use polymer monoliths to purify large quantities of antibody with defined clinical and performance requirements. Functional monolithic supports have attracted a great deal of attention as they offer practical advantages for antibody purification, such as more rapid analysis, smaller sample volume requirements and the opportunity for a greater target molecule enrichment. This review focuses on the development of synthetic and natural polymer-based monoliths for antibody purification. The materials and methods employed in monolith production are discussed, highlighting the properties of each system. We also review the structural characterization techniques available using monolithic systems and their performance under different chromatographic approaches to antibody capture and release. Finally, a summary of monolithic platforms developed for antibody separation is presented, as well as expected trends in research to solve current and future challenges in this field. This review comprises a comprehensive analysis of proposed solutions highlighting the remarkable potential of monolithic platforms.

Barroso, T, Roque ACA, Aguiar-Ricardo A.  2012.  Bioinspired and Sustainable Chitosan Based Monoliths for Antibody Capture and Release. RSC ADV. 2(30):11285-11294. AbstractWebsite

Chitosan-based monoliths activated by plasma technology induced the coupling of a robust biomimetic ligand, previously reported as an artificial Protein A, with high yields while minimizing the environmental impact of the procedure. Due to the high porosity, good mechanical and tunable physicochemical properties of the affinity chitosan-based monoliths, it is possible to achieve high binding capacities (150 ± 10 mg antibody per gram support), and to recover 90 ± 5% of the bound protein with 98% purity directly from cell-culture extracts. Therefore, the chitosan-based monoliths prepared by clean processes exhibit a remarkable performance for the one-step capture and recovery of pure antibodies or other biological molecules with biopharmaceutical relevance.

Barroso, T, Lourenço A, Araújo M, Bonifácio VDB, Roque ACA, Aguiar-Ricardo A.  2013.  A green approach toward antibody purification: a sustainable biomimetic ligand for direct immobilization on (bio)polymeric supports. Journal of Molecular Recognition. 26(12):662-671.
Barroso, T, Temtem M, Hussain A, Aguiar-Ricardo A, Roque ACA.  2010.  Preparation and characterization of a cellulose affinity membrane for human immunoglobulin G (IgG) purification, feb. Journal of Membrane Science. 348:224–230., Number 1-2 AbstractWebsite

This paper reports the design, preparation and characterization of cellulose affinity membranes for antibody purification using a new methodology. Cellulose membranes were prepared from polymer-ionic liquid solutions, namely 1-butyl-3-methylimidazolium chloride {([BMIM][Cl])}, by the water induced phase inversion process. After functionalization with a synthetic ligand 2-(3-aminophenol)-6-(4-amino-1-naphthol)-4-chloro-s-triazine (ligand 22/8), these were evaluated as affinity supports for human immunoglobulin G {(IgG).} Membranes were characterized in terms of morphology {(SEM)}, porosity (mercury porosimetry), hydrophilicity (contact angle measurement), transport properties (permeability) and mechanical performance {(DMA).} Membranes prepared with varying cellulose contents (5 and 10&\#xa0;wt.% cellulose in ionic liquid solutions) lead to films with different properties. The 10&\#xa0;wt.% cellulose membrane presented enhanced morphological and mechanical properties, however, the morphology of this membrane was significantly altered after ligand coupling. Adsorption isotherms for human {IgG} onto 10&\#xa0;wt.% matrix activated with ligand 22/8 were obtained. Preliminary results showed that the bovine serum albumin {(BSA)}, a model impurity, did not adsorb onto the membrane while up to 6&\#xa0;mg {IgG/g} was bound and 2&\#xa0;mg {IgG/g} recovered.

Barroso, T, Branco RJF, Aguiar‐Ricardo A, Roque ACA.  2014.  Structural evaluation of an alternative Protein A biomimetic ligand for antibody purification. Journal of Computer-Aided Molecular Design. 28(1):25-34. AbstractWebsite

Affinity chromatography is one of the most common techniques employed at the industrial-scale for antibody purification. In particular, the purification of human immunoglobulin G (hIgG) has gained relevance with the immobilization of its natural binding counterpart—Staphylococcus aureus Protein A (SpA) or with the recent development of biomimetic affinity ligands, namely triazine-based ligands. These ligands have been developed in order to overcome economic and leaching issues associated to SpA. The most recent triazine-based ligand—TPN-BM, came up as an analogue of 2-(3-amino-phenol)-6-(4-amino-1-naphthol)-4-chloro-sym-triazine ligand also known as ligand 22/8 with improved physico-chemical properties and a greener synthetic route. This work intends to evaluate the potential of TPN-BM as an alternative affinity ligand towards antibody recognition and binding, namely IgG, at an atomic level, since it has already been tested, after immobilization onto chitosan-based monoliths and demonstrated interesting affinity behaviour for this purpose. Herein, combining automated molecular docking and molecular dynamics simulations it was predicted that TPN-BM has high propensity to bind IgG through the same binding site found in the crystallographic structure of SpA_IgG complex, as well as theoretically predicted for ligand 22/8_IgG complex. Furthermore, it was found that TPN-BM established preferential interactions with aromatic residues at the Fab domain (Trp 50, Tyr 53, Tyr 98 and Trp 100), while in the Fc domain the main interactions are based on hydrogen bonds with pH sensitive residues at operational regime for binding and elution like histidines (His 460, His 464, His 466). Moreover, the pH dependence of TPN-BM_IgG complex formation was more evident for the Fc domain, where at pH 3 the protonation state and consequently the charge alteration of histidine residues located at the IgG binding site induced ligand detachment which explains the optimal elution condition at this pH observed experimentally.

Batalha, ÍL, Roque ACA.  2016.  Petasis-Ugi ligands: New affinity tools for the enrichment of phosphorylated peptides. Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences. 1031:86–93.: Elsevier B.V. AbstractWebsite

Affinity chromatography is a widespread technique for the enrichment and isolation of biologics, which relies on the selective and reversible interaction between affinity ligands and target molecules. Small synthetic affinity ligands are valuable alternatives due to their robustness, low cost and fast ligand development. This work reports, for the first time, the use of a sequential Petasis-Ugi multicomponent reaction to generate rationally designed solid-phase combinatorial libraries of small synthetic ligands, which can be screened for the selection of new affinity adsorbents towards biological targets. As a proof of concept, the Petasis-Ugi reaction was here employed in the discovery of affinity ligands suitable for phosphopeptide enrichment. A combinatorial library of 84 ligands was designed, synthesized on a chromatographic solid support and screened in situ for the specific binding of phosphopeptides binding human BRCA1C-terminal domains. The success of the reaction on the chromatographic matrix was confirmed by both inductively coupled plasma atomic emission spectroscopy and fluorescence microscopy. Three lead ligands were identified due to their superior performance in terms of binding capacity and selectivity towards the phosphorylated moiety on peptides, which showed the feasibility of the Petasis-Ugi reaction for affinity ligand development.

Batalha, IL, Lowe CR, Roque ACA.  2012.  Platforms for enrichment of phosphorylated proteins and peptides in proteomics. Trends in Biotechnology. 30(2):100-110. AbstractWebsite

Protein phosphorylation is a complex and highly dynamic process involved in numerous biological events. Abnormal phosphorylation is one of the underlying mechanisms for the development of cancer and metabolic disorders. The identification and absolute quantification of specific phospho-signatures can help elucidate protein functions in signaling pathways and facilitate the development of new and personalized diagnostic and therapeutic tools. This review presents a variety of strategies currently utilized for the enrichment of phosphorylated proteins and peptides before mass spectrometry analysis during proteomic studies. The investigation of specific affinity reagents, allied to the integration of different enrichment processes, is triggering the development of more selective, rapid and cost-effective high-throughput automated platforms.

Batalha, IL, Hussain A, Roque ACA.  2010.  Gum Arabic coated magnetic nanoparticles with affinity ligands specific for antibodies, oct. Journal of Molecular Recognition. 23:462–471., Number 5 AbstractWebsite

A novel magnetic support based on gum Arabic {(GA)} coated iron oxide magnetic nanoparticles {(MNP)} has been endowed with affinity properties towards immunoglobulin G {(IgG)} molecules. The success of the in situ triazine ligand synthesis was confirmed by fluorescence assays. Two synthetic ligands previously developed for binding to {IgG}, named as ligand 22/8 (artificial Protein A) and ligand 8/7 (artificial Protein L) were immobilized on to {MNPs} coated with {GA} {(MNP\_GA).} The dimension of the particles core was not affected by the surface functionalization with {GA} and triazine ligands. The hydrodynamic diameters of the magnetic supports indicate that the coupling of {GA} leads to the formation of larger agglomerates of particles with about 1 microm, but the introduction of the triazine ligands leads to a decrease on {MNPs} size. The non-functionalized {MNP\_GA} bound 28 mg {IgG/g}, two times less than bare {MNP} (60 mg {IgG/g).} {MNP\_GA} modified with ligand 22/8 bound 133 mg {IgG/g} support, twice higher than the value obtained for ligand 8/7 magnetic adsorbents (65 mg/g). Supports modified with ligand 22/8 were selected to study the adsorption and the elution of {IgG.} The adsorption of human {IgG} on this support followed a Langmuir behavior with a Q(máx) of 344 mg {IgG/g} support and K(a) of 1.5 x 10(5) M. The studies on different elution conditions indicated that although the 0.05 M citrate buffer {(pH} 3) presented good recovery yields (elution 64% of bound protein), there was occurrence of iron leaching at this acidic {pH.} Therefore, a potential alternative would be to elute bound protein with a 0.05 M {glycine-NaOH} {(pH} 11) buffer.

Batalha, ÍL, Roque ACA.  2016.  Phosphopeptide Enrichment Using Various Magnetic Nanocomposites: An Overview. Phospho-Proteomics. 1355(Methods in Molecular Biology):193–209. AbstractWebsite

Magnetic nanocomposites are hybrid structures consisting of an iron oxide (Fe3O4 /$\gamma$-Fe2O3 ) superparamagnetic core and a coating shell which presents affi nity for a specifi c target molecule. Within the scope of phosphopeptide enrichment, the magnetic core is usually fi rst functionalized with an intermediate layer of silica or carbon to improve dispersibility and increase specifi c area, and then with an outer layer of a phosphate-affi nity material. Fe3O4 -coating materials include metal oxides, rare earth metal-based compounds, immobilized-metal ions, polymers, and many others. This chapter provides a generic overview of the different materials that can be found in literature and their advantages and drawbacks.

Batalha, IL, Lychko I, Branco RJF, Iranzo O, Roque ACA.  2019.  β-Hairpins as peptidomimetics of human phosphoprotein-binding domains. Organic & Biomolecular Chemistry. 17:3996-4004. AbstractWebsite

Phosphoprotein-binding domains interact with cognate phosphorylated targets ruling several biological processes. The impairment of such interactions is often associated with disease development, namely cancer. The breast cancer susceptibility gene 1 (BRCA1) C-terminal (BRCT) domain is involved in the control of complex signaling networks of the DNA damage response. The capture and identification of BRCT-binding proteins and peptides may be used for the development of new diagnostic tools for diseases with abnormal phosphorylation profiles. Here we show that designed cyclic β-hairpin structures can be used as peptidomimetics of the BRCT domain, with high selectivity in binding to a target phosphorylated peptide. The amino acid residues and spatial constraints involved in the interaction between a phosphorylated peptide (GK14-P) and the BRCT domain were identified and crafted onto a 14-mer β-hairpin template in silico. Several cyclic peptides models were designed and their binding towards the target peptide and other phosphorylated peptides evaluated through virtual screening. Selected cyclic peptides were then synthesized, purified and characterized. The high affinity and selectivity of the lead cyclic peptide towards the target phosphopeptide was confirmed, and the possibility to capture it using affinity chromatography demonstrated. This work paves the way for the development of cyclic β-hairpin peptidomimetics as a novel class of affinity reagents for the highly selective identification and capture of target molecules.

Batalha, IL, Zhou H, Lilley K, Lowe CR, Roque ACA.  2016.  Mimicking nature: Phosphopeptide enrichment using combinatorial libraries of affinity ligands. Journal of Chromatography A. 1457:76–87.: Elsevier B.V. AbstractWebsite

Phosphorylation is a reversible post-translational modification of proteins that controls a plethora of cellular processes and triggers specific physiological responses, for which there is a need to develop tools to characterize phosphorylated targets efficiently. Here, a combinatorial library of triazine-based synthetic ligands comprising 64 small molecules has been rationally designed, synthesized and screened for the enrichment of phosphorylated peptides. The lead candidate (coined A8A3), composed of histidine and phenylalanine mimetic components, showed high binding capacity and selectivity for binding mono- and multi-phosphorylated peptides at pH 3. Ligand A8A3 was coupled onto both cross-linked agarose and magnetic nanoparticles, presenting higher binding capacities (100-fold higher) when immobilized on the magnetic support. The magnetic adsorbent was further screened against a tryptic digest of two phosphorylated proteins ($\alpha$- and $\beta$-caseins) and one non-phosphorylated protein (bovine serum albumin, BSA). The MALDI-TOF mass spectra of the eluted peptides allowed the identification of nine phosphopeptides, comprising both mono- and multi-phosphorylated peptides.

Bicho, A, Peça IN, Roque ACA, Cardoso MM.  2010.  Anti-CD8 conjugated nanoparticles to target mammalian cells expressing CD8. International Journal of Pharmaceutics. 399:80–86., Number 1-2 AbstractWebsite

This work aimed at the development of targeted drug delivery systems using nanoparticles fused with antibodies. The antibody anti-human {CD8} was coupled onto {PLGA} nanoparticles, and the ability of these particles to specifically target cells expressing {CD8} was studied. The obtained particles were found to be of spherical shape exhibiting a size between 350 and 600 nm. In vitro experiments with different cellular cultures {(TE671}, {CHO} and {HEK293)} using unmodified nanoparticles containing rhodamine have shown that particles were present on their surface within 48 h of incubation. In vitro tests using {anti-CD8} conjugated nanoparticles in {CHO} cell cultures indicated that all transfected cells which express {CD8} show these particles on their surface within 1h of incubation. These results demonstrated that, in a shorter time, the produced particles can target cells expressing {CD8} on their surface which offers the ability to reduce drug side effects. The antibody-coupled nanoparticles represent a promising approach to improve the efficacy of active targeting for lymphoblastic leukaemia therapy.

Bicho, A, Roque ACA, Cardoso AS, Domingos P, Batalha ÍL.  2010.  In vitro studies with mammalian cell lines and gum arabic‐coated magnetic nanoparticles. Journal of Molecular Recognition. 23:536–542., Number 6 AbstractWebsite

Iron oxide magnetic nanoparticles {(MNPs)} were synthesized by the chemical co-precipitation method and coated with gum arabic {(GA)} by physical adsorption and covalent attachment. Cultures of mammalian cell lines {(HEK293}, {CHO} and {TE671)} were grown in the presence of uncoated and {GA-coated} {MNPs.} Cellular growth was followed by optical microscopy in order to assess the proportion of cells with particles, alterations in cellular density and the presence of debris. The in vitro assays demonstrated that cells from different origins are affected differently by the presence of the nanoparticles. Also, the methods followed for {GA} coating of {MNPs} endow distinct surface characteristics that probably underlie the observed differences when in contact with the cells. In general, the nanoparticles to which the {GA} was adsorbed had a smaller ability to attach to the cells' surface and to compromise the viability of the cultures. Copyright © 2010 John Wiley & Sons, Ltd.

Borlido, L, Azevedo AM, Roque ACA, Aires-Barros MR.  2013.  Magnetic separations in biotechnology. Biotechnology Advances. 31(8):1374-1385. AbstractWebsite

Magnetic separations are probably one of the most versatile separation processes in biotechnology as they are able to purify cells, viruses, proteins and nucleic acids directly from crude samples. The fast and gentle process in combination with its easy scale-up and automation provide unique advantages over other separation techniques. In the midst of this process are the magnetic adsorbents tailored for the envisioned target and whose complex synthesis spans over multiple fields of science. In this context, this article reviews both the synthesis and tailoring of magnetic adsorbents for bioseparations as well as their ultimate application.

Borlido, L, Azevedo AM, Sousa AG, Oliveira PH, Roque ACA, Aires-Barros MR.  2012.  Fishing human monoclonal antibodies from a CHO cell supernatant with boronic acid magnetic particles. Journal of Chromatography B. 903:163-170. AbstractWebsite

In this work we have evaluated the potential of boronic acid functionalized magnetic particles for the one-step capture of a human monoclonal antibody (mAb) from a Chinese hamster ovary (CHO) cell culture supernatant. For comparison, Protein A coated magnetic particles were also used. The most important factor influencing the overall process yield and product purity in boronic acid particles was found to be the binding pH. Basic pH values promoted higher purities while resulting in decreased yields due to the competing effects of molecules such as glucose and lactate present in the cell culture supernatant. After optimization, the particles were successfully used in a multi-cycle purification process of the mAb from the CHO feedstock. Boronic acid particles were able to achieve an average overall yield of 86% with 88% removal of CHO host cell proteins (HCP) when the binding was performed at pH 7.4, while at pH 8.5 these values were 58% and 97%, respectively. In both cases, genomic DNA removal was in excess of 97%. Comparatively, Protein A particles recorded an average overall yield of 80% and an HCP removal greater than 99%. The adsorption of the mAb to the boronic acid particles was shown to be mediated by strong affinity interactions. Overall, boronic acid based purification processes can offer a cost-effective alternative to Protein A as the direct capturing step from the mammalian cell culture.

Borlido, L, Azevedo AM, Roque ACA, Aires-Barros MR.  2011.  Potential of boronic acid functionalized magnetic particles in the adsorption of human antibodies under mammalian cell culture conditions. Journal of Chromatography A. 1218(43):7821-7827. AbstractWebsite

In this work, we systematically evaluated the potential of using boronic acid functionalized magnetic particles in the capturing of human immunoglobulin G under typical mammalian cell culture conditions. For comparison, Protein A coated magnetic particles were also used. The binding pH was found to significantly influence the adsorption isotherms of boronic acid particles with the higher capacities (0.216 g IgG/g support) being observed at pH 7.4. Comparatively, this value was 0.109 g IgG/g support, for Protein A particles under the same conditions. Both particles revealed very fast adsorption kinetics with more than 70% of the maximum binding capacity being achieved in a few seconds. The effect of glucose and lactate, which are known to interact with boronic acid, was evaluated. For glucose, the binding capacity was significantly influenced by the pH and decreased as pH increased. At pH 9.5, a 70% lower binding capacity was observed for glucose concentrations as low as 0.5 g/l. The effect of lactate was less pronounced and almost pH independent reaching at most 20% decrease in binding capacity. Nevertheless, the effect of both molecules was always lower at pH 7.4. The optimization of the elution conditions enabled complete recovery of bound IgG from boronic acid particles using 50mM Tris-HCl, 200 mM sorbitol, 200 mM NaCl at pH 8.5.

Borlido, L, Moura L, Azevedo AM, Roque ACA, Aires‐Barros MR, Farinha JPS.  2013.  Stimuli‐Responsive magnetic nanoparticles for monoclonal antibody purification. Biotechnology Journal. 8(6):709–717. AbstractWebsite

Monoclonal antibodies (mAbs) are important therapeutic proteins. One of the challenges facing large-scale production of monoclonal antibodies is the capacity bottleneck in downstream processing, which can be circumvented by using magnetic stimuli-responsive polymer nanoparticles. In this work, stimuli-responsive magnetic particles composed of a magnetic poly(methyl methacrylate) core with a poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) shell cross-linked with N, N'-methylenebisacrylamide were prepared by miniemulsion polymerization. The particles were shown to have an average hydrodynamic diameter of 317 nm at 18°C, which decreased to 277 nm at 41°C due to the collapse of the thermo-responsive shell. The particles were superparamagnetic in behavior and exhibited a saturation magnetization of 12.6 emu/g. Subsequently, we evaluated the potential of these negatively charged stimuli-responsive magnetic particles in the purification of a monoclonal antibody from a diafiltered CHO cell culture supernatant by cation exchange. The adsorption of antibodies onto P(NIPAM-co-AA)-coated nanoparticles was highly selective and allowed for the recovery of approximately 94% of the mAb. Different elution strategies were employed providing highly pure mAb fractions with host cell protein (HCP) removal greater than 98%. By exploring the stimuli-responsive properties of the particles, shorter magnetic separation times were possible without significant differences in product yield and purity.

Branco, RJF, Dias AMGC, Roque ACA.  2012.  Understanding the molecular recognition between antibody fragments and protein A biomimetic ligand. Journal of Chromatography A. 1244:106-115. AbstractWebsite

Affinity chromatography with protein A from Staphylococcus aureus (SpA) is the most widespread and
accepted methodology for antibody capture during the downstream process of antibody manufacturing.
A triazine based ligand (ligand 22/8) was previously developed as an inexpensive and robust alternative
to SpA chromatography (Li et al. [12] and Teng et al. [11]). Despite the experimental success, there is no
structural information on the binding modes of ligand 22/8 to antibodies, namely to Immunoglobulin G
(IgG) molecules and fragments. In this work, we addressed this issue by a molecular docking approach
allied to molecular dynamics simulations. Theoretical results confirmed the preference of the synthetic
ligand to bind IgG through the binding site found in the crystallographic structure of the natural complex
between SpA and the Fc fragment of IgG. Our studies also suggested other unknown “hot-spots” for
specific binding of the affinity ligand at the hinge between VH and CH1 domains of Fab fragment. The best
docking poses were further analysed by molecular dynamics studies at three different protonation states
(pH 3, 7 and 11). The main interactions between ligand 22/8 and the IgG fragments found at pH 7 were
weaker at pH 3 and pH 11 and in these conditions the ligand start losing tight contact with the binding
site, corroborating the experimental evidence for protein elution from the chromatographic adsorbents
at these pH conditions.