Binding characteristics of staphylococcal protein A and streptococcal protein G for fragment crystallizable portion of human immunoglobulin G

A facile and effective electrochemical immunosensor based on controlled and oriented immobilization of natural antibodies for sensitive detection of aflatoxin B1

Aflatoxin B1 (AFB1) is one of the most common and harmful toxins in agricultural products, and the development of a sensitive, simple, and accurate detection method for AFB1 is crucial for ensuring continuous monitoring and safeguarding food safety. Herein, we describe a facile and effective electrochemical immunosensor for ultrasensitive detection of AFB1. In this framework, a novel Fc-specific cysteine (Cys)-modified antibody was first fabricated by employing photoaffinity labeling technique, which enables antibodies to be directionally immobilized onto a bare gold electrode via Au-sulfhydryl interaction. The proposed immunosensor exhibited detection limits (LODs) of 0.054 and 0.019 ng mL-1 for direct competitive and sandwich-type competitive assays, respectively. Notably, these LODs were approximately 8-fold and 10-fold lower, respectively, compared to those achieved with randomly immobilized antibodies. The proposed immunosensor demonstrated excellent stability and reproducibility, along with high sensitivity, accuracy, and precision in AFB1 detection, suggesting its significant potential for applications in food safety applications.

Development of a bioluminescent immunoassay based on Fc-specific conjugated antibody-nanoluciferase immunoreagents for determining aflatoxin B1

Aflatoxin B1 (AFB1) is a potent carcinogen, and is among the most hazardous mycotoxins in agricultural products. Therefore, the development of sensitive and convenient detection methods for AFB1 is significant for food safety against mycotoxins. Herein, a bioluminescent enzyme immunoassay (BLEIA) was developed for ultrasensitive detection of AFB1, based on the novel Fc-specific antibody-nanoluciferase (Ab-Nluc) conjugates which were fabricated using an IgG-binding protein-assisted photo-conjugation strategy. In indirect competitive immunoassay format, the proposed BLEIA exhibited the detection limit of 0.0232 ng mL-1, which was 37.4-fold lower than that obtained using the classical enzyme-linked immunosorbent assay (ELISA) based on Ab-horseradish peroxidase (Ab-HRP) chemical conjugates (0.868 ng mL-1). Meanwhile, the BLEIA exhibited high accuracy and precision. Thus, the proposed Fc-specific Ab-Nluc conjugates-based BLEIA provides an ultrasensitive and reliable method for detecting toxins and has potential for use in food safety monitoring.

p54-Fc-Labeled Gold Nanoparticle-Based Lateral Flow Strip-Assisted Portable Devices for Rapid and Quantitative Point-of-Care Detection of ASFV Antibodies

In this study, a novel rapid immunochromatographic (IC) test for African swine fever virus (ASFV) antibodies is presented. An immunochromatographic test (IC) is a detection technique that combines membrane chromatography with immunolabeling. This approach saves time for antibody preparation, resulting in a shorter production cycle. p54 is an important structural protein of African swine fever, and an ideal protein for serotype diagnosis. Gold nanoparticles are attached to the ASFV p54-Fc fusion protein, and the ASFV-specific antigen p54 and Staphylococcus aureus protein A (SPA) are labeled on a nitrocellulose membrane, at positions T and C, respectively. We developed a SPA double sandwich IC test strip, and assessed its feasibility using ASFV p54 and p54-Fc fusion proteins as antigens. ASFV p54 and p54-Fc fusion proteins were expressed and purified. A sandwich cross-flow detection method for p54, which is the primary structural protein of ASFV, was established, using colloidal gold conjugation. Our method can detect ASFV antibodies in field serum samples in about 15 min using a portable colloidal gold detector, demonstrating high specificity and sensitivity (1:320), and the coincidence rate was 98% using a commercial ELISA kit. The dilution of the serum sample can be determined by substituting the absorbance (T-line) interpreted by portable devices into the calibration curve function formula of an African swine fever virus standard serum. In summary, our method is rapid, cost-effective, precise, and highly selective. Additionally, it introduces a new approach for constructing IC test strips using SPA protein without antibody preparation, making it a reliable on-site antibody test for ASFV.

Optical biosensing of monkeypox virus using novel recombinant silica-binding proteins for site-directed antibody immobilization

The efficient immobilization of capture antibodies is crucial for timely pathogen detection during global pandemic outbreaks. Therefore, we proposed a silica-binding protein featuring core functional domains (cSP). It comprises a peptide with a silica-binding tag designed to adhere to silica surfaces and tandem protein G fragments (2C2) for effective antibody capture. This innovation facilitates precise site-directed immobilization of antibodies onto silica surfaces. We applied cSP to silica-coated optical fibers, creating a fiber-optic biolayer interferometer (FO-BLI) biosensor capable of monitoring the monkeypox virus (MPXV) protein A29L in spiked clinical samples to rapidly detect the MPXV. The cSP-based FO-BLI biosensor for MPXV demonstrated a limit of detection (LOD) of 0.62 ng/mL in buffer, comparable to the 0.52 ng/mL LOD achieved using a conventional streptavidin (SA)-based FO-BLI biosensor. Furthermore, it achieved LODs of 0.77 ng/mL in spiked serum and 0.80 ng/mL in spiked saliva, exhibiting no cross-reactivity with other viral antigens. The MPXV detection process was completed within 14 min. We further proposed a cSP-based multi-virus biosensor strategy capable of detecting various pandemic strains, such as MPXV, the latest coronavirus disease (COVID) variants, and influenza A protein, to extend its versatility. The proposed cSP-modified FO-BLI biosensor has a high potential for rapidly and accurately detecting MPXV antigens, making valuable contributions to epidemiological studies.

Fabrication of cysteine-modified antibodies with Fc-specific conjugation for covalent and oriented immobilization of native antibodies

Covalent and oriented immobilization of antibodies (Abs) can substantially improve the sensitivity and stability of solid-phase immunoassays. By modifying the natural Abs with functional groups that provide unique handles for further conjugation, Abs could be immobilized onto the solid matrices with uniform orientation. Herein, an effective approach for Fc-specific modification of Abs was developed for the oriented and covalent immobilization of Abs. Twelve photoreactive Z-domain variants, incorporated with a photoactivable probe (p-benzoyl-L-phenylalanine, Bpa) at different positions and carrying a C-terminal Cys-tag (i.e. ZBpa-Cys variants), were individually constructed and produced in Escherichia coli and tested for photo-cross-linking to various IgGs. The different ZBpa-Cys variants demonstrated large differences in photo-conjugation efficiency for the tested IgGs. The conjugation efficiencies of 17thZBpa-Cys ranged from 90 % to nearly 100 % for rabbit IgG and mouse IgG2a, IgG2b and IgG3. Other variants, including 5thZBpa-Cys, 18thZBpa-Cys, 32thZBpa-Cys, and 35thZBpa-Cys, also displayed conjugation efficiencies of 61 %-83 % for mouse IgG1, IgG2a and IgG3. Subsequently, the photo-modified Abs, namely IgG-Cys conjugates, were covalently immobilized onto a maleimide group-functionalized solid-phase carrier on the basis of the reaction of sulfhydryl and maleimide. Thus, a generic platform for the controlled and oriented immobilization of Abs was developed, and the efficacy and potential of the proposed approach for sensitive immunoassays was demonstrated by detecting human α-fetoprotein.

The Potential of Single-Chain Variable Fragment Antibody: Role in Future Therapeutic and Diagnostic Biologics

The advancement of genetic engineering has revolutionized the field of immunology by allowing the utilization of intrinsic antibody structures. One of the biologics that are being produced by recombinant antibody technology is single-chain fragments variable (scFv). Genes of variable regions, the heavy and light chains that are genetically linked into a single transcript by a short flexible linker peptide, are used to generate this fragment from cellular and synthetic libraries. The specificity and affinity of these molecules are comparable to those of parental antibodies. Fusion with marker proteins and other potent molecules improves their stability, circulation half-life, activity, and efficient purification. Besides, this review comprises construction protocols, therapeutics, and diagnostic applications of scFv, as well as related challenges. Nonetheless, there are still issues with efficacy, stability, safety, intracellular administration, and production costs that need to be addressed.

Transforming waste into valuables: Preparation and evaluation of dual-ligand hydrophobic charge-induction chromatography using two poor performing ligands

In conventional chromatographic ligand screening, underperforming ligands are often dismissed. However, this practice may inadvertently overlook potential opportunities. This study aims to investigate whether these underperforming ligands can be repurposed as valuable assets. Hydrophobic charge-induction chromatography (HCIC) is chosen as the validation target for its potential as an innovative chromatographic mode. A novel dual-ligand approach is employed, combining two suboptimal ligands (5-Aminobenzimidazole and Tryptamine) to explore enhanced performance and optimization prospects. Various dual-ligand HCIC resins with different ligand densities were synthesized by adjusting the ligand ratio and concentration. The resins were characterized to assess appearance, functional groups, and pore features using SEM, FTIR, and ISEC techniques. Performance assessments were conducted using single-ligand mode resins as controls, evaluating the selectivity against human immunoglobulin G and human serum albumin. Static adsorption experiments were performed to understand pH and salt influence on adsorption. Breakthrough experiments were conducted to assess dynamic adsorption capacity of the novel resin. Finally, chromatographic separation using human serum was performed to evaluate the purity and yield of the resin. Results indicated that the dual-ligand HCIC resin designed for human antibodies demonstrates exceptional selectivity, surpassing not only single ligand states but also outperforming certain high-performing ligand types, particularly under specific salt and pH conditions. Ultimately, a high yield of 83.9 % and purity of 96.7 % were achieved in the separation of hIgG from human serum with the dual-ligand HCIC, significantly superior to the single-ligand resins. In conclusion, through rational design and proper operational conditions, the dual-ligand mode can revitalize underutilized ligands, potentially introducing novel and promising chromatographic modes.

Mechanism Analysis of Antimicrobial Peptide NoPv1 Related to Potato Late Blight through a Computer-Aided Study

Phytophthora infestans (Mont.) de Bary, the oomycotic pathogen responsible for potato late blight, is the most devastating disease of potato production. The primary pesticides used to control oomycosis are phenyl amide fungicides, which cause environmental pollution and toxic residues harmful to both human and animal health. To address this, an antimicrobial peptide, NoPv1, has been screened to target Plasmopara viticola cellulose synthase 2 (PvCesA2) to inhibit the growth of Phytophthora infestans (P. infestans). In this study, we employed AlphaFold2 to predict the three-dimensional structure of PvCesA2 along with NoPv peptides. Subsequently, utilizing computational methods, we dissected the interaction mechanism between PvCesA2 and these peptides. Based on this analysis, we performed a saturation mutation of NoPv1 and successfully obtained the double mutants DP1 and DP2 with a higher affinity for PvCesA2. Meanwhile, dynamics simulations revealed that both DP1 and DP2 utilize a mechanism akin to the barrel-stave model for penetrating the cell membrane. Furthermore, the predicted results showed that the antimicrobial activity of DP1 was superior to that of NoPv1 without being toxic to human cells. These findings may offer insights for advancing the development of eco-friendly pesticides targeting various oomycete diseases, including late blight.

Construction of a versatile fusion protein for targeted therapy and immunotherapy

Antibody (Ab)-based drugs have been widely used in targeted therapies and immunotherapies, leading to significant improvements in tumor therapy. However, the failure of Ab therapy due to the loss of target antigens or Ab modifications that affect its function limits its application. In this study, we expanded the application of antibodies (Abs) by constructing a fusion protein as a versatile tool for Ab-based target cell detection, delivery, and therapy. We first constructed a SpaC Catcher (SpaCC for short) fusion protein that included the C domains of Staphylococcal protein A (SpaC) and the SpyCatcher. SpaCC conjugated with SpyTag-X (S-X) to form the SpaCC-S-X complex, which binds non-covalently to an Ab to form the Ab-SpaCC-S-X protein complex. The "X" can be a variety of small molecules such as fluoresceins, cell-penetrating peptide TAT, Monomethyl auristatin E (MMAE), and DNA. We found that Ab-SpaCC-S-FITC(-TAT) could be used for target cell detection and delivery. Besides, we synthesized the Ab-SpaCC-SN3-MMAE complex by linking Ab with MMAE by SpaCC, which improved the cytotoxicity of small molecule toxins. Moreover, we constructed an Ab-DNA complex by conjugating SpaCC with the aptamer (Ap) and found that Ab-SpaCC-SN3-Ap boosted the tumor-killing function of T-cells by retargeting tumor cells. Thus, we developed a multifunctional tool that could be used for targeted therapies and immunotherapies, providing a cheap and convenient novel drug development strategy.

In-line buffer exchange in the coupling of Protein A chromatography with weak cation exchange chromatography for the determination of charge variants of immunoglobulin G derived from chinese hamster ovary cell cultures

Immunoglobulin G (IgG) is the most common monoclonal antibody (mAb) grown for therapeutic applications. While IgG is often selectively isolated from cell lines using protein A (ProA) chromatography, this is only a stepping stone for complete characterization. Further classification can be obtained from weak cation exchange chromatography (WCX) to determine IgG charge variant distributions. The charge variants of monoclonal antibodies can influence the stability and efficacy in vivo, and deviations in charge heterogeneity are often cell-specific and sensitive to upstream process variability. Current methods to characterize IgG charge variants are often performed off-line, meaning that the IgG eluate from the ProA separation is collected, diluted to adjust the pH, and then transferred to the WCX separation, adding time, complexity, and potential contamination to the sample analysis process. More recently, reports have appeared to streamline this separation using in-line two-dimensional liquid chromatography (2D-LC). Presented here is a novel, 2D-LC coupling of ProA in the first dimension (1D) and WCX in the second dimension (2D) chromatography. As anticipated, the initial direct column coupling proved to be challenging due to the pH incompatibility between the mobile phases for the two stages. To solve the solvent compatibility issue, a size exclusion column was placed in the switching valve loop of the 2D-LC instrument to act as a means for the on-line solvent exchange. The efficacy of the methodology presented was confirmed through a charge variant determination using the NIST monoclonal antibody standard (NIST mAb), yielding correct acidic, main, and basic variant compositions. The methodology was employed to determine the charge variant profile of IgG from an in-house cultured Chinese hamster ovary (CHO) cell supernatant. It is believed that this methodology can be easily implemented to provide higher-throughput assessment of IgG charge variants for process monitoring and cell line development.

Recombinant streptococcal protein G-modified metal-organic framework ZIF-8 for the highly selective purification of immunoglobulin G from human serum

A novel solid phase extractant His-rSPG@ZIF-8 was prepared by covalently coupling recombinant streptococcal protein G (His-rSPG) with ZIF-8. The His-rSPG@ZIF-8 composite was characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Due to the specific binding between the immunoglobulin binding region of His-rSPG and the Fc region of immunoglobulin G (IgG), the His-rSPG@ZIF-8 composite demonstrated exceptional selectivity in adsorbing IgG. In Britton-Robinson buffer (BR buffer) with a salt concentration of 500 mmol L-1 (0.04 mol L-1, pH 8.0), the His-rSPG@ZIF-8 composite exhibited a remarkable adsorption efficiency of 99.8 % for 0.05 mg of the composite on 200 μL of IgG solution (100 μg mL-1). The adsorption behavior of the His-rSPG@ZIF-8 composite aligns with the Langmuir adsorption model, and the theoretical maximum adsorption capacity is 1428.6 mg g-1. The adsorbed IgG molecules were successfully eluted using a SDS solution (0.5 %, m/m), resulting in a recovery rate of 91.2 %. Indeed, the His-rSPG@ZIF-8 composite was successfully utilized for the isolation and purification of IgG from human serum samples. The obtained IgG exhibited high purity, as confirmed by SDS-PAGE analysis. Additionally, LC-MS/MS analysis was employed to identify the human serum proteins following the adsorption and elution process using the His-rSPG@ZIF-8 composite material. The results revealed that the recovered solution contained an impressive content of immunoglobulin, accounting for 62.4 % of the total protein content. Furthermore, this process also led to the significant enrichment of low abundance proteins such as Serpin B4 and Cofilin-1. Consequently, the His-rSPG@ZIF-8 composite holds great promise for applications such as IgG purification and immunoassays. At the same time, it expands the application of metal-organic frameworks in the field of proteomics.

Production and Purification of Antibodies in Chinese Hamster Ovary Cells

Antibodies are versatile biological molecules with widespread applications in research and medicine. This protocol outlines the generation of monoclonal IgG antibodies from Chinese hamster ovary cells. It includes steps for cell maintenance, transient transfection, and antibody purification via protein A affinity chromatography. The methods described are intended for the production of milligram amounts of protein but can be adapted for most small- to mid-scale applications.

The immune evasion roles of Staphylococcus aureus protein A and impact on vaccine development

While Staphylococcus aureus (S. aureus) bacteria are part of the human commensal flora, opportunistic invasion following breach of the epithelial layers can lead to a wide array of infection syndromes at both local and distant sites. Despite ubiquitous exposure from early infancy, the life-long risk of opportunistic infection is facilitated by a broad repertoire of S. aureus virulence proteins. These proteins play a key role in inhibiting development of a long-term protective immune response by mechanisms ranging from dysregulation of the complement cascade to the disruption of leukocyte migration. In this review we describe the recent progress made in dissecting S. aureus immune evasion, focusing on the role of the superantigen, staphylococcal protein A (SpA). Evasion of the normal human immune response drives the ability of S. aureus to cause infection, often recurrently, and is also thought to be a major hindrance in the development of effective vaccination strategies. Understanding the role of S. aureus virulence protein and determining methods overcoming or subverting these mechanisms could lead to much-needed breakthroughs in vaccine and monoclonal antibody development.

Exploring the inhibitory potential of novel piperidine-derivatives against main protease (Mpro) of SARS-CoV-2: A hybrid approach consisting of molecular docking, MD simulations and MMPBSA analysis

In the current study, a hybrid computational approach consisting of different computational methods to explore the molecular electronic structures, bioactivity and therapeutic potential of piperidine compounds against SARS-CoV-2. The quantum chemical methods are used to study electronic structures of designed derivatives, molecular docking methods are used to see the most potential docking interactions for main protease (M^Pro) of SARS-CoV-2 while molecular dynamic and MMPBSA analyses are performed in bulk water solvation process to mimic real protein like aqueous environment and effectiveness of docked complexes. We designed and optimized piperidine derivatives from experimentally known precursor using quantum chemical methods. The UV-Visible, IR, molecular orbitals, molecular electrostatic plots, and global chemical reactivity descriptors are carried out which illustrate that the designed compounds are kinetically stable and reactive. The results of MD simulations and binding free energy revealed that all the complex systems possess adequate dynamic stability, and flexibility based on their RMSD, RMSF, radius of gyration, and hydrogen bond analysis. The computed net binding free energy ( Δ G b i n d ) as calculated by MMPBSA method for the complexes showed the values of -4.29 kcal.mol^-1 for P1, -5.52 kcal.mol^-1 for P2, -6.12 kcal.mol^-1 for P3, -6.35 kcal.mol^-1 for P4, -5.19 kcal.mol^-1 for P5, 3.09 kcal.mol^-1 for P6, -6.78 kcal.mol^-1 for P7, and -6.29 kcal.mol^-1 for P8.The ADMET analysis further confirmed that none of among the designed ligands violates the Lipinski rule of five (RO5). The current comprehensive investigation predicts that all our designed compounds are recommended as prospective therapeutic drugs against M^pro of SARS-CoV-2 and it provokes the scientific community to further perform their in-vitro analysis.

Real-time kinetics and affinity analysis of the interaction between protein A and immunoglobulins G derived from different species on silica colloidal crystal films

Kinetic and affinity analysis of protein interactions reveals information on their related activities in biological processes. Herein, we established a system for evaluating the kinetics and affinity of the interaction between protein A and various IgG species on the surface of silica spheres of silica colloidal crystal (SCC) films by the extraordinary optical interference capabilities of 190 nm silica spheres after self-assembly. The equilibrium association constant (KA) was calculated by the equilibrium Langmuir model and nonlinear least-squares analysis of time-dependent data. The relative protein A/IgG binding affinity is human > rabbit >cow >goat. In addition, the competitive interaction of distinct species of IgG with protein A at the interface of SCC films was studied and performed. These findings may help with the use of protein A and other recognition components in a number of sensor types. Furthermore, this research might offer a novel approach to determining the kinetics and affinity of proteins on the surface of spheres particles, which may contribute to the development of the application of spheres particles in pharmaceutical science, biomedical engineering, and other techniques.

Understanding gilteritinib resistance to FLT3-F691L mutation through an integrated computational strategy

FMS-like tyrosine kinase 3 (FLT3) serves as an important drug target for acute myeloid leukemia (AML), and gene mutations of FLT3 have been closely associated with AML patients with an incidence rate of ~ 30%. However, the mechanism of the clinically relevant F691L gatekeeper mutation conferred resistance to the drug gilteritinib remained poorly understood. In this study, multiple microsecond molecular dynamics (MD) simulations, end-point free energy calculations, and dynamic correlated and network analyses were performed to investigate the molecular basis of gilteritinib resistance to the FLT3-F691L mutation. The simulations revealed that the resistant mutation largely induced the conformational changes of the activation loop (A-loop), the phosphate-binding loop, and the helix αC of the FLT3 protein. The binding abilities of the gilteritinib to the wild-type and the F691L mutant were different through the binding free energy prediction. The simulation results further indicated that the driving force to determine the binding affinity of gilteritinib was derived from the differences in the energy terms of electrostatic and van der Waals interactions. Moreover, the per-residue free energy decomposition suggested that the four residues (Phe803, Gly831, Leu832, and Ala833) located at the A-loop of FLT3 had a significant impact on the binding affinity of gilteritinib to the F691L mutant. This study may provide useful information for the design of novel FLT3 inhibitors specially targeting the F691L gatekeeper mutant.

Mechanistic Insights into the Mechanism of Inhibitor Selectivity toward the Dark Kinase STK17B against Its High Homology STK17A

As a member of the death-associated protein kinase (DAPK) family, STK17B plays an important role in the regulation of cellular apoptosis and has been considered as a promising drug target for hepatocellular carcinoma. However, the highly conserved ATP-binding site of protein kinases represents a challenge to design selective inhibitors for a specific DAPK isoform. In this study, molecular docking, multiple large-scale molecular dynamics (MD) simulations, and binding free energy calculations were performed to decipher the molecular mechanism of the binding selectivity of PKIS43 toward STK17B against its high homology STK17A. MD simulations revealed that STK17A underwent a significant conformational arrangement of the activation loop compared to STK17B. The binding free energy predictions suggested that the driving force to control the binding selectivity of PKIS43 was derived from the difference in the protein–ligand electrostatic interactions. Furthermore, the per-residue free energy decomposition unveiled that the energy contribution from Arg41 at the phosphate-binding loop of STK17B was the determinant factor responsible for the binding specificity of PKIS43. This study may provide useful information for the rational design of novel and potent selective inhibitors toward STK17B.

Detergent micelle conjugates containing amino acid monomers allow purification of human IgG near neutral pH

Industrial scale production of therapeutic monoclonal antibodies (mAbs) is commonly achieved with Protein A chromatography, a process that requires exposure of the antibody to strongly acidic conditions during the eluting step. Exposure to acid inactivates virus contaminants but may, in parallel, lead to antibody aggregation that must be eliminated or kept at acceptably low levels. This report seeks to provide a practical method for overcoming a long-standing problem. We show how Brij-O20 detergent micelles, conjugated by the amphiphilic [(bathophenanthroline)₃:Fe²⁺] complex in the presence of amino acid monomers: phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), isoleucine (Ile) or valine (Val), efficiently capture polyclonal human IgG (hIgG) at neutral pH and allow its recovery by extraction either at pH 4 (85-97% yield) or at pH 6.3 (72-84% yield). Of the five amino acid monomers surveyed, Phe or Tyr produced the highest overall process yield at both pH 4 and 6.3. The monomeric state of the purified hIgG's was confirmed by dynamic light scattering (DLS). Potential advantages of the purification method are discussed.

Functionalisation of Inorganic Material Surfaces with Staphylococcus Protein A: A Molecular Dynamics Study

Staphylococcus protein A (SpA) is found in the cell wall of Staphylococcus aureus bacteria. Its ability to bind to the constant Fc regions of antibodies means it is useful for antibody extraction, and further integration with inorganic materials can lead to the development of diagnostics and therapeutics. We have investigated the adsorption of SpA on inorganic surface models such as experimentally relevant negatively charged silica, as well as positively charged and neutral surfaces, by use of fully atomistic molecular dynamics simulations. We have found that SpA, which is itself negatively charged at pH7, is able to adsorb on all our surface models. However, adsorption on charged surfaces is more specific in terms of protein orientation compared to a neutral Au (111) surface, while the protein structure is generally well maintained in all cases. The results indicate that SpA adsorption is optimal on the siloxide-rich silica surface, which is negative at pH7 since this keeps the Fc binding regions free to interact with other species in solution. Due to the dominant role of electrostatics, the results are transferable to other inorganic materials and pave the way for new diagnostic and therapeutic designs where SpA might be used to conjugate antibodies to nanoparticles.